Annals of Clinical Biochemistry: An international journal of biochemistry in medicine http://acb.sagepub.com/

Analytical Reviews in Clinical Biochemistry: The Quantitative Analysis of Cholesterol W Richmond Ann Clin Biochem 1992 29: 577 DOI: 10.1177/000456329202900601 The online version of this article can be found at: http://acb.sagepub.com/content/29/6/577.citation

Published by: http://www.sagepublications.com

On behalf of: Association for Clinical Biochemistry and Laboratory Medicine

Netherlands Society for Clinical Chemistry and Laboratory Japan Society of Clinical Chemistry

Additional services and information for Annals of Clinical Biochemistry: An international journal of biochemistry in medicine can be found at: Email Alerts: http://acb.sagepub.com/cgi/alerts Subscriptions: http://acb.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav

>> Version of Record - Nov 1, 1992 What is This?

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013

Ann CUn Biochem 1992; 29: 577-597

Review Article

Analytical reviews in clinical biochemistry: the quantitative analysis of cholesterol W Richmond From the Department of Chemical Pathology, St Mary's Hospital, Praed Street, London W21PG, UK Studies on the occurrence and chemical nature of cholesterol can be traced'v to the observation, circa 1733, of the partial solubility of gallstones in alcohol! and the subsequent crystallization" of an unsaponifiable substance' from this source. It was named cholesterine by Chevreul" in 1816according to its origin [Greek: chole, bile, steros, solid] and first identified in human blood in 1838by Lecanu.? Its discovery in atheromatous arteries by Vogel in 18438 was an early indication of the pathological significance of this important compound. Introduction of the name cholesterol and identification of cholesterol esters in plasma followed Berthelot's work (1859) showing 'cholesterine' to be an alcohol. 9 The exact empirical formulae was established by Reinitzer in 1888. 10 Elucidation of the chemically reactive portions of the molecule was completed by 1904 with the identification of a double bond!' and demonstration that the alcohol group was secondary. 12 The colour reactions of cholesterol with strong acids were first noted by Salkowski (1872).13 Many variants of this type of reaction were reported and applied empirically to quantitative analysis over the next century as will be discussed in detail later. The immense task of elucidating the structural formula of cholesterol began circa 1900 and took 30 years work by the most notable chemists to unravel. Weiland and Windaus received the Nobel prize in 1928 for their brilliant work in this field. X-ray crystallographic studies by Bernal in Cambridge (1932)14 indicated however that the Weiland structure gave a molecule of the wrong dimensions. Rosenheim and King working at Mill Hill used this information and additional chemical evidence produced by Diels and Gadke" to deduce the correct cyclopentano phenanthrene structure in 1932. 16 •17 This review was commissioned by the Analytical Methods Working Party of the Scientific Committee of the Association of Clinical Biochemists. The views expressed are those of the author and are not necessarily those of the Scientific Committee.

Cholesterol was first demonstrated in plasma lipoprotein complexes by Macheboeuf (1929).18 Developments in electrophoresis (Tiselius, 1941),19 analytical ultracentrifugation (Gofman et ai, 1949),20 and preparative ultracentrifugation (Havel et al, 1955)21 demonstrated the existence of different lipoprotein fractions and enabled their classification according to electrophoretic mobility and density. Low density lipoproteins and high density lipoproteins were shown to be the major cholesterol transporting fractions. By 1950 a great deal of evidence had accrued to support the hypothesis that serum cholesterol concentrations tended to be higher in individuals presenting with coronary heart disease than in normals matched for age, sex, weight, etc.22 ,23 Furthermore, it had become evidentthat atherosclerosis was prominent in disease states, notably diabetes" and nephrosis,2s accompanied by hypercholesterolaemia. The relationship between low density lipoproteins and atherosclerosis had been demonstrated by Gofman using the ultracentrifugation techniques developed by his group." He claimed that the correlation between these measurements and atherosclerosis was much closer than that between blood cholesterol concentrations and this disease. The majority opinion of the United States National Heart Advisory Council, following a large cooperative study completed in 1956, was that lipoprotein measurements presented no advantage over cholesterol analysis in identifying individuals prone to develop coronary heart disease." Cholesterol measurements were thus established as an important aspect of aetiological and epidemiological studies while lipoprotein studies would make an important contribution to understanding the complexities of cholesterol transport and lipoprotein metabolism. THE MEASUREMENT OF TOTAL AND FREE CHOLESTEROL IN SERUM The chemical approach The reaction of cholesterol with strong acid under dehydrating conditions to give coloured products 577

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013

578

Richmond

has been widely used for the quantitative determination of cholesterol. Of the many variants of this reaction reported, the LiebermannBurchard and Zak reactions have found the widest application in clinical analysis. The former was described initially by Liebermanrr? in 1885, and applied to cholesterol analysis shortly after by Burchard.P Cholesterol was allowed to react with sulphuric acid and acetic anhydride in chloroform solvent in the original studies, but the Liebermann-Burchard reaction is now carried out in an acetic acid-sulphuric acid-acetic anhydride medium. The Zak reaction was first applied to cholesterol analysis by Zlatkis et al. in 195329 and is carried out in an acetic acid-sulphuric acid medium. In this reaction, however, ferric ions must be present to obtain the required coloured species as explained below. Early mechanistic studies on colour production by the action of acids on cholesterol have been reviewed by Kritchevesky.f It was suggested that the mechanism of the sulphuric acid-initiated colour reactions of cholesterol involves an initial dehydration to cholestadiene followed by the formation of coloured sulphonated dimers which can undergo further polymerization. Subsequent studies suggested that a more probable mechanism involved the oxidation of cholesterol to a pentadiene.P More recently, Burke et al. 31 have presented evidence for the mechanisms of the Zak and Liebermann-Burchard colour reactions proposed in Fig. 1. According to these proposals, which are based on the correlation of spectral and mass spectrophotometric data with S02 and Fe 2+ measurements, both reactions have a common initial step, i.e. protonation of the 3{j-hydroxy group in cholesterol and subsequent loss of water to give the carbonium ion of 3,5-cholestadiene. Serial oxidation of this carbonium ion, by S03 in the Liebermann-Burchard reaction and Fe 3+ in the Zak reaction, yields the cholestapolyene carbonium ions shown. Thus it was suggested that the red product (>.. max 536 nm) typically measured in the Zak reaction is predominantly the cholestatetraenylic species, and the blue-green product in the Liebermann-Burchard reaction (>.. max 620 nm) is predominantly the pentaenylic species. These studies indicate that the colour reactions of cholesterol produce a number of products with varying absorptivities. This is an undesirable situation in quantitative analysis, and indicates the need to use these reactions under strictly controlled conditions. Furthermore, these reactions are very non-specific and require some

Dienylic ccticn A mcx- 412 nm

Pentcenylic cction A mcx- 620 nm

~ •••

T2

+ Fe

., + .- •• Trienylic cction Amox-47Bnm

SO OH 2

~! ...

+S0 2

~

I

"'" ~ Cholestchexcene sulphcnic ccid A mcx-410nm

!

,~

~

Tetrceny lic cction Amcx- 563nm

FIGURE 1. Proposed mechanisms of the Zak and Liebermann-Burchard reaction. JJ

degree of purification of the analyte before they can be applied successfully to the quantitative measurement of cholesterol in biological tissues or fluids. Despite these limitations methods have been proposed for the determination of cholesterol in serum based on the colour reactions described above. In some, colourimetric reactions have been applied directly to serum 29,32-34 while in others cholesterol is isolated from serum and purified to various degrees prior to colourlmetric measurement. In many procedures cholesterol is separated from protein by solvent extraction prior to colourimetric determination.P 4· 6 mmol/L, in type III hyperlipidaemia, or when chylomicrons are present in the sample. Alternatively, LDL cholesterol can be calculated from the difference between measurements of cholesterol before and after selective precipitation of LDL.19S-198 LDL cholesterol, derived from three measurements by the Friedwald formula or by two measurements in direct precipitation procedures, is a rather imprecise measurement and there has been much debate about the validity of the Friedwald formula. 199-202 None the less, it is a bonus when calculated from three useful measurements and has found acceptance in assigning risk and making decisions on therapy. 171 Total HDL cholesterol can be measured with acceptable precision.P! Accuracy is difficult to define, however, because of heterogeneity HDL and the qualitative differences between fractions obtained by selective precipitation and ultracentrifugation. For example Lp(a) , an apoBcontaining lipoprotein, is isolated in the HDL fraction prepared by ultracentrifugation but is removed together with LDL and VLDL in precipitation procedures.P' Apo E containing HDL is precipitated by dextran sulphate-Mgt" but not by the heparin-Mn-:' reagent.P' Considerable matrix effects are evident in control materials (author's unpublished studies) and significant differences are obtained on patients' samples with different precipitation procedures although the results are highly correlated. 184.18S.187.20S Rate zonapos and density gradientl06 ultracentrifugation studies on HDL sub fractions prepared by precipitation indicate that although the ultracentrifugation and precipitation techniques give similar results for total HDL cholesterol, they assigned different distributions to HDL subfraction cholesterol. No interferences from precipitating reagents have been reported in the reference cholesterol method. Manganese ions can cause turbidity to develop in certain enzymic reagent systems.P? This can be readily overcome by incorporation of EDTA in the reagent. Dextran sulphate of high molecular weight (500 (00) has been shown to give low results in another enzymic system!" possibly by inhibition of pancreatic cholesterol esterase. 208 No other interferences by the precipitating reagents in cholesterol assays have been reported. It has been demonstrated, however, that increased plasma concentrations of EDTA resulting from incomplete filling of blood

collection tubes cause serious overestimations of HDL3 cholesterol due to chelation of divalent cations in the precipitating reagents and consequently incomplete precipitation of HDL2. 209 Despite these analytical limitations a low total HDL cholesterol remains an important risk factor for coronary heart disease''" particularly in women"? and individuals with elevated plasma triglyceride concentrations.i!' HDL2 cholesterol, being derived from the difference between two measurements at relatively low concentration, is an imprecise measurement and is not likely to be accepted as a diagnostic or prognostic test until the physiological functions of HDL subfractions are more clearly understood. Factors to be considered in the selection of precipitation procedures for HDL cholesterol measurement include: (a) The quality and availability of precipitation reagents (b) Freedom from interference in cholesterol reagent systems (c) The ability to give stable precipitates at high triglyceride concentrations (d) The degree of dilution of sample by the precipitating reagent Polyethylene glycol (PEG) and phosphotungstateMg2+ reagents are readily available in 'kit' form. These systems have no reported interferences with cholesterol reagents and are tolerant of high sample triglyceride concentrations. The sample is diluted threefold by these precipitants, however, which necessitates measuring cholesterol at low concentrations. The viscosity of the PEG solutions is a potential source of imprecision and/or inaccuracy with some pipetting systems. An advantage of the heparin-Mn-" and Dextran Sulphate-Mg-" systems is their low dilution of sample (10%). However, they are less tolerant of high triglyceride concentrations. Mn 2+ ions can interfere with some cholesterol reagents and the source of heparin of defined activity is critical. Similarly, the molecular weight of dextran sulphate is important. The author has found the procedure described by Warnick et a/. 186 using dextran sulphate of 50 ()()() molecular weight [Dextralip 50, from Sochibo, Villacoublay, France] to be a most robust procedure providing an economic method with minimal sample dilution.

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013

Analytical reviews in clinical biochemistry THE BLOOD SAMPLE FOR LIPID AND LIPOPROTEIN STUDIES The selection, collection, and storage of blood samples for lipoprotein analyses has been extensively reviewed by Bachorik.i'f A brief summary is given here. Patients should be following their normal eating habits and should not be investigated during an acute illness or pregnancy. For the assessment of cholesterol status alone a fasting sample is not essential. A 12 h fast is mandatory for a profile including triglyceride measurements or lipoprotein studies. Venipuncture should be carried out on patients who have been in the sitting position for at least 5 min. The tourniquet should be used for as brief a period as possible and released before withdrawing the sample. Either plasma or serum can be used but it should be noted that the osmotic effects of low molecular weight anticoagulants shift water from erythrocytes to plasma causing a reduction in lipoprotein concentrations.i" Samples anticoagulated with EDTA at a final concetltration of 1· 5 mg/mL give results 3070 lower than simultaneously obtained serum samples. Blood bottles should be filled to the correct volume to minimize variation caused by this effect. Variations in sample EDTA concentrations can also seriously affect selective lipoprotein precipitating procedures involving divalent cations.P? EDTA does have the advantage however of chelating heavy metals such as Cu 2 + that promote auto-oxidation of unsaturated fatty acids and cholesterol. EDTA is also an inhibitor of phospholipase C that can arise from bacterial contamination. EDTA is therefore the preferred anticoagulant if samples have to be stored prior to lipoprotein analysis and can be added to serum samples for this purpose. Samples should be allowed to clot in glass tubes at room temperature for 45 min. Serum or plasma should be separated from cells within 3 h. Plasma can be stored at 4 DC for total cholesterol and triglyceride analyses or frozen at - 20 DC or below for longer periods. There is a great deal of conflicting evidence, however, on the stability of HDL during frozen storage.!" Lipoprotein fractionation should be done as soon as possible on fresh samples. CONCLUSION The complex structure and heterogeneity of lipoproteins present the major difficulty in the formulation of enzymic reagent systems which are

591

required to disrupt these complexes, achieve complete hydrolysis of cholesterol esters, and ensure the quantitative oxidation of cholesterol by cholesterol oxidase. Matrix effects introduced by freezing, lyophilization or the addition of nonhuman materials make it difficult to produce calibration and control sera which do not introduce varying degrees of bias in different reagent systems. Consequently, although excellent precision can be achieved with the many enzymic reagent kits now available, accuracy and inter-laboratory consensus are more elusive. Laboratories should therefore be careful to select calibrators and reagent systems with proven performance from reputable manufacturers and apply these on sound analytical principles to minimize interference. Accuracy should be assessed with certified reference materials and by comparison of results on fresh patient sera with those obtained by a reference procedure or a procedure with proven accuracy. After a century of use in clinical analysis the application of the Liebermann-Burchard reaction, with all its limitations, in reference procedures should also be reviewed. Accurate spectrophotometric measurement of ~4 cholestenone following chemical hydrolysis of cholesterol esters, extraction and enzymic oxidation of cholesterol as proposed by Trinder'P' deserves serious consideration as a practicable alternative. This procedure is within the scope of every laboratory with an adequate spectrophotometer and could be refined by the application of HPLC to the measurement of ~4 cholestenone. It is also evident that excellent accuracy and precision are attainable by gas chromatography and it is likely that this technique will find increasing application in reference laboratories.

REFERENCES I Dam H. In: Cook RP, ed. Cholesterol. New York: Academic Press, 1958 2 Kritchevsky D. In: Cholesterol. New York: Wiley 1958 • 3 Va1lsnieri A. Opere Fisco-mediche, Stampate and Manoscritte, Vol. 3. Venice: Coleti, 1733; 594 4 De Fourcroy AF. De la substance feuillettee et crystalline contenue dans les calculs biliares, et de la natures des concentrations cystiques crista1isees. Ann Chim 1789; 3: 242-52 5 Chevreul ME. Researches chimiques sur plusieurs corps gras, et particulierement sur leurs combinations avec les alcalis. Cinquieme Memoire. Ann Chim 1815; 95: 5-50

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013

592

Richmond

6 Chevreul ME. Sixieme Memoire, Examen des graisse d'homrne, de mouton, de boeuf', de jaguar et d'oie. Ann Chim et Phys 1816; 2: 339-72 7 Lecanu LR. Etudes chimique sur le san humain. Ann Chim Phys 1838; 67: 54-70 8 Vogel J. leones Histologies Pathologiae. Leipzig: Leopold Voss 1843; 101-2 9 Berthelot M. Sur plusiers alcools nouveaux. Ann Chim Phys 1859; 56: 51-98 10 Reinitzer F. Beitrage Zur Kenntniss des Cholesterins. Sitzber Akad Wiss Wein, Math-Naturw, KI Abt i 1888; 97; 167-87 II Wislicenus J, Moldenhauer W. Ueber das cholesterindibromur. Ann Chim 1868; 146: 175-80 12 Diels 0, Aberhalden E. Zur Kenntniss des Cholesterins. Ber 1904; 37: 3092-103 13 Salkowski E. Kleinere Mittheilungen physiologischchemischen Inhalts (II). Pfluger's Arch ges Phsiol 1872; 6: 207-22 14 Bernal JD. Crystal structures of vitamin D and related compounds. Nature 1932; 129: 277-8 15 Diels 0, Gadke W. Uber die Bildung von Chrysen bei der Dehydrierung des Cholesterins. Ber 1927; 60: 140-7 16 Rosenheim 0, King H. The ring system of sterols and bile acids. Nature 1932; 130: 315 17 Rosenheim 0, King H. The ring system of sterols and bile acids. J Soc Chem Ind (Land) 1932; 51: 464-6 18 Macheboeuf M. Researches sur les phosphoaminolipides et les sterides due serum et du plasma sanguins 1&11. Bull Soc Chim Bioi 1929; 11: 268-93 & 493 19 Blix G, Tiselius A, Svensson H. Lipids and polysaccharides in electrophoretically separated blood serum proteins. J Bioi Chem 1941; 137: 485-94 20 Gofman JW, Lindgren FT, Elliott H. Ultracentrifugal studies of lipoproteins of human serum. J Bioi Chem 1949; 179: 973-9 21 Havel RJ, Eder HA, Bragdon JH. The distribution and chemical composition of ultracentrifugally separated lipoproteins and human serum. J Clin Invest 1955; 34: 1345-53 22 Morrison LM, Hall L, Chancey AL. Cholesterol metabolism; blood serum cholesterol and ester levels in 200 cases of acute coronary thrombosis. Am J Med Sci 1948; 216: 32-8 23 Steiner A, Kendall FE, Mathers JAL. The abnormal lipid pattern in patients with coronary arteriosclerosis. Circulation 1952; 5: 605-8 24 Liewbow 1M, Hellerstein HK. Cardiac complications of diabetes mellitus. Am J Med 1949; 7: 660-70 25 Gofman JW, Jones HB, Lindgren FT, Lyon TP, Elliot HA, Strisower B. Blood lipids and human atherosclerosis. Circulation 1950; 2: 161-78 26 Gofman JW, Hanig M, Jones HB, et al. Evaluation of serum lipoprotein and cholesterol measurements as predictors of clinical complications of atherosclerosis. Circulation 1956; 14: 691-741 27 Liebermann NC. Uber das Oxychinoterpen. Ber DIsch Chem Ges 1885; 18: 1803-9 28 Burchard H. Deitrage zur Kenntnis des Cholesterins. Chem Zentralbl 1890; 61: 25-7

29 Ziatkis A, Zak B, Boyle AJ. A new method for direct determination of serum cholesterol. J Lab Clin Med 1953; 41: 486-92 30 Brieskorn CH, Hoffmann H. Biet Chem Farbreaktion Libermann-Burchard 1964; 41: 486-92 31 Burke RW, Diamondstone BI, Velapoldi RA, Menis O. Mechanisms of the Liebermann-Burchard and Zak color reactions for cholesterol. C/in Chem 1974; 20: 794-801 32 Kenny AP, Jamieson A. Automated method for the direct determination of total serum cholesterol. Clin Chim Acta 1964; 10: 536-43 33 Annan W, Isherwood DM. An automated method for the direct determination of total serum cholesterol. J Med Lab Technol 1969; 26: 202-11 34 Holub WR, Galli FA. The determination of cholesterol in blood. J Bioi Chem 1972; 18: 239-43 35 Bloor WR. The determination of cholesterol in blood. J Bioi Chem 1916; 24: 227-31 36 Zak B, Dickenman RC, White EG, Burnett H, Cherney P J. Rapid esimation of free and total cholesterol. Am J Clin Pathol 1954; 24: 1307-15 38 Levine IB, Zak B. Automated determination of serum total cholesterol. C/in Chim Acta 1964; 10: 381-4 39 Abell LL, Levy BB, Brodie BB, Kendall FE. A simplified method for the estimation of total cholesterol in serum and demonstrated of its specificity. J Bioi Chem 1952; 195: 357-66 40 Brown WD. Errors in the determination of serum cholesterol. Aust J Exp Bioi Med 1961; 39: 209-22 41 Hermann RG. Determination of serum and tissue cholesterol. Proc Soc Exp Bioi Med 1957; 94: 503-5 42 Schoenheirner R, Sperry WM. A micro method for the determination of free and combined cholesterol. J Bioi Chem 1934; 106: 745 43 Sperry WM, Webb MA. A revision of the Schoenheimer-Sperry method for cholesterol determination. J Bioi Chem 1950; 187: 97-106 44 Duncan IW, Mather A, Cooper GR. The procedure for the proposed cholesterol reference method. (Available on request from Dr G R Cooper, Clinical Chemistry Division, Centre for Disease Control, Atlanta, GA 3033, USA) 1982 45 Cooper GR, Smith Sl, Duncan IW, et al, Interlaboratory testing of the transferability of a candidate reference method for total cholesterol in serum. Clin Chem 1986; 32: 921-9 46 Lipid Research Clinics Programme. The Lipid Research Clinics Coronary Primary Prevention Trial results. I. Reduction in incidence of coronary heart disease. JAm Med Assoc 1984; 251: 351-64 47 Lipid Research Clinics Programme. The Lipid Research Clinics Coronary Prevention Trial results: II. The relationship of reduction incidence of coronary heart disease to cholesterol lowering. JAm Med Assoc 1984; 251: 365-74 48 Anon. Lipid and lipoprotein analysis. In: Manual of Laboratory Operations, Lipid Research Clinics Program, Vol. I, Publication No. (NIH) 75628, ed. Department of Health, Education & Welfare, Washington DC, 1974

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013

Analytical reviews in clinical biochemistry 49 Lippel K, Ahmed S, Albers JJ. Bachorik P, Cooper G, Helms R, Williams J. Analytical performance and comparability of the determination of cholesterol by 12 lipid-research clinics. Clin Chem 1977; 23: 1744-52 50 Cham BE, Hurwood 11, Knowles BR, Powell LW. Rapid, sensitive method for the separation of free cholesterol from ester cholesterol. Clin Chim Acta 1973; 49:.109-13 51 Ham AB. Cholesterol: factors in methology and a survey of normal levels. Am J Med Techno/1962; 29: 99-106 52 Vanzetti G. Methods photometrique de dosage du cholesterol dans Ie serum. Clin Chim Act 1964; 10: 389-405 53 Tonks DB. The estimation of cholesterol in serum: a classification and critical review of methods. Clin Biochem 1967; 1: 12-29 54 Fasce CF, Vanderlinde RE. Factors affecting the results of serum cholesterol determination: an interlaboratory evaluation. Clin Chem 1972; 18: 901-8 55 Brown SS. Notes on the quality of performance of serum cholesterol assays. Ann Clin Biochem 1973; 10: 146-54 56 Derks HJGM, van Heiningen A, Koedan HC. Gaschromatographic determination of cholesterol in serum: candidate reference method. Clin Chem 1985; 31: 691-4 57 Driscoll JL, Aubuchon D, Descoteaux M, Martin HF. Seminautomated, specific routine serum cholesterol determination by gas-liquid chromatography. Anal Chem 1971; 43: 1196-200 58 Brunnkereeft JWI, Boerma GJM, Leijnse B. Direct determination of total serum cholesterol by oncolum gas-liquid chromatographic analysis without previous derivatisation compared with WHO-CDC reference method. Ann Clin Biochem 1983; 20: 360-3 59 Harris PA, Harris KL. Quantitative GLC analysis of plasma cholesterol. J Pharm Sci 1974; 63: 781-4 60 Morin RJ, Elms N1. Rapid microanalysis of cholesterol in bile and serum by gas chromatography. Ann Clin Lab Sci 1975; 5: 52-6 61 Ishikawa TT, MacGee J, Morrison JA, Glueck C1. Quantitative analysis of cholesterol in 5 to 20 ILl of plasma. J Lipid Res 1974; 15: 286-91 62 MacGee J, Ishikawa T, Miller W, Evans G, Steiner P, Glueck CJ. A micromethod for analysis of total plasma cholesterol using gas-liquid chromatography. J Lab Clin Med 1973; 82: 656-62 63 Blomhoff JP. Serum cholesterol determination by gas-liquid chromatography. Clin Chim Acta 1973; 43: 596-9 64 MacGee J. Characterisation of mammalian tissues and microorganisms by gas-liquid chromatography. J Gas Chromatogr 1968; 6: 48-52 65 Van Den Heuvel WJ, Sjovall J, Horning EC. Gaschromatographic behaviour of trifluoracetoxy steroids. Biochim Biophys Acta 1961; 48: 596-9 66 Kuksis A, Stachnyk 0, Holub B1. Improved quantitation of plasma lipids by direct gasliquid chromatography. J Lipid Res 1969; 10: 660-7

593

67 Gambert P, Lallement C, Archambault A, et al. Assessment of serum cholesterol by two methods: gas-liquid chromatography on a capillary colum and chemical ionization-mass fragmentography with isotopic dilution of 3,4-13C cholesterol as internal standard. J Chromatogr 1979; 162: 1-6 68 Cohen A, Hertz HS, Mandel J, et al. Total serum cholesterol by isotope dilution/mass spectrometry: A candidate definitive method. Clin Chem 1980; 26: 854-60 69 Bjorkhem R, Bloomstrand R, Svesson L. Serum cholesterol determination by mass fragmentography, Clin Chim Acta 1974; 54: 185-93 70 Siekmann L, Huskis KP, Breuer H. Determination of cholesterol in serum using mass fragmentography-a Reference Method in clinical chemistry. Fresenius Z Anal Chem 1976; 279: 145-6 71 Wolthers BG, Hindrinks FR, Muskiet FAJ, Groen A. Mass fragmentographic analysis of total cholesterol in serum using a heptadeuterated internal standard. Clin Chim Acta 1980; 103: 305-15 72 Freundenthal, Derks HJGM, Gramberg LG. ten Hove GJ, Klaasen R. Isotope dilution mass spectrometry of cholesterol in serum. Biomed Mass Spectrom 1981; 8: 5-9 73 Schaffer R, Sniegoski LT, Welch MJ, et al. Comparison of two isotope dilution/mass spectrometric methods for determination of total serum cholesterol. Clin Chem 1982; 28: 5-8 74 Pelletier 0, Wright LA, Breckenridge WC. Isotope dilution/mass spectrometry of serum cholesterol with (3,4-13C) cholesterol: proposed definitive method. Clin Chem 1987; 33: 1403-11 75 Duncan IW, Culbreth PH, Burtis CA. Determination of free, total, and esterified cholesterol by high-performance liquid chromatography. J Chromatogr 1979; 162: 281-92 76 Takatsu A, Nishi S. Total cholesterol in serum determined by isotope dilution/mass spectrometry, with liquid-chromatographic separation. Clin Chem 1987; 33: 1113-17 77 Sohngen LL. Benzine, petroleum, paraffmol und paraffin ab kohlenstoff-und energiequelle fur mikroken. Zentralbl Bakteriol Parasitenk 1913; 37: 595-609 78 Tak JD. Bacteria decomposing cholesterol. Antonie van Leeuwenhoek 1942; 8: 32-40 79 Turfitt GE. The microbiological degradation of steroids. II. Oxidation of cholesterol by Proactinomyces spp. Biochem J 1944; 38: 492-6 80 Stadtman TC, Cherkes A, Anfinsen CB. Studies on the microbiological degradation of cholesterol. J Bioi Chem 1954; 206: 511-23 81 Whitmarsh JM. Intermediates of microbiological metabolism of cholesterol. Biochem J 1964; 90: 23-4 82 Sih CJ, Wang KC, Tai HH. Acid intermediates in the microbiological cleavage of the cholesterol side chain. JAm Chem Soc 1967; 89: 1956-7 83 Sih CJ, Tai HH, Tsong YY. The mechanism of microbiol conversion of cholesterol into 17-keto steroids. JAm Chem Soc 1967; 89: 1957-8 84 Nasgasawa M, Bae M, Tamura G, Arima K. Microbial transformations of steroids. II. Cleavage of sterol side chains by microorganisms. Agricult Bioi Chem 1969; 33: 1644

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013

594

Richmond

85 Peterson GE, Davis JR. Cholesterol utilisation by Streptomyces spp. Steroids 1964; 4: 677-97 86 Schatz A, Savard K, Pinter II. The ability of soil microorganisms to decompose steroids. J Bacteriol 1949; 58: 117-25 87 Stadtman TC. Preparation and assay of cholesterol and ergosterol. In: Methods in Enzymology, III. Colowick SP, Kaplan NO, eds., New York: Academic Press, 1957; 392-4 88 Flegg HM. An investigation of the determination of serum cholesterol by an enzymatic method. Ann Clin Biochem 1973; 10: 79-84 89 Richmond W. The development of an enzymic technique for the assay of cholesterol in biological fluids (Abstract). Scand J Clin Lab Invest (Suppl) 1972; 126: 325 90 Richmond W. Preparation and properties of a cholesterol oxidase from Nocardia sp. and its application to the enzymic assay of total cholesterol in serum. Clin Chem 1973; 19: 1350-1356 91 Richmond W. An enzymic approach to the automated analysis of cholesterol in serum. PhD Thesis: CNAA/MRC Clinical Research Centrel University College London 92 Buckland BC, Richmond W, Dunnill P, Lilly MD. The large-scale isolation of intracellular microbial enzymes: cholesterol oxidase from nocardia. In: Industrial Aspects of Biochemistry. Spencer B, ed. FEBS 1974; 65-79 93 Fukuda H, Kawakami Y, Nakanura S. A method to screen anticholesterol substances produced by microbes and a new cholesterol oxidase produced by Streptomyces violascens. Chem Pharm Bull (Tokyo) 1973; 21: 2057-60 94 Uwajima T, Yagi H, Nakamura S, Terada O. Isolation and crystallisation of extracellular 3 betahydroxysteroid oxidase of Brevibacterium steroIicum nov. sp. Agricult Bioi Chem 1973;37: 2345-50 95 Tomioka H, Kagawa M, Nakamura S. Some enzymic properties of 3 Beta-hydroxysteroid oxidase produced by Streptomyces violascens. J Biochem (Tokyo) 1976; 79: 903-15 96 Uwajima T, Yagi H, Terada O. Properties of crystalline 3 beta-hydroxysteroid oxidase of Brevi-bacterium sterolicum. Agricult Bioi Chem 1974; 38: 1149-56 97 Wentz PW, Cross RE, Savory 1. An integrated approach to lipid profiling: enzymatic determination of cholesterol and triglycerides with a centrifugal analyzer. Clin Chem 1976; 22: 188-92 98 Lie RF, Schmitz J, Pierre KJ, Goochman N. Cholesterol oxidase-based determination, by continuous-flow analysis, of total and free cholesterol in serum. Clin Chem 1976; 22: 1627-30 99 Smith AG, Brooks CJW. Cholesterol oxidases: properties and applications. J Steroid Biochem 1976; 7: 705-13 100 Brooks CJW, Smiht AG. Cholesterol oxidase: further studies of substrate specificity in relation to the analytical characterisation of steroids. J Chromatogr 1975; 112: 499-511 101 Anon. Cholesterol oxidase from Nocardia erythropolis. In: Methods ofEnzymatic Analysis, Vol. I, 2nd edn Bergmeyer HU, ed. New York: Academic Press, 1974; 440

102 Smith AG, Brooks CJW. Application of cholesterol oxidase in the analysis of steroids. J Chromatogr 1974; 101: 373-8 103 Slickers KA. Enzyme-linked assays for cholesterol. CRC Crit Rev Clin Lab Sci 1977; 8: 193-212 104 Wybenga DR, Inkpen JA. Lipids 19. In: Clinical Chemistry, Principles and Techniques, 2nd edn 1974; 1429-1431. Edited by: Henry RJ, Canon DC, Winkelman JW. Hagerstown, Md: Harper & Row 105 Koehler AE, Hill E. 7-dehydrocholesterol in human serum. Amer Soc Bioi Chem Fed Proc 1953; 12: 232-3 106 Trinder P. Oxidase determination of plasma cholesterol as cholest-4-en-3-one using isooctane extraction. Ann Clin Biochem 1981; 18: 64-70 107 Connor WE. Dietary sterols: their relationship to atherosclerosis. J Amer Diet Assoc 1968; 552: 202-8 108 Salen G, Aherns Jnr EH, Grundy SM. Metabolism of (j-sitosterol in man. J Clin Invest 1953; 49: 952-67 109 Bhattacharyya AK, Connor WE. Beta-sistosterolemia and xanthomatosis. A newly described lipid storage disease in two sisters. J Clin Invest 1974; 53: 1033-43 110 Vahouny GV, Treadwell CR. Enzymatic synthesis and hydrolysis of cholesterol esters. In: Methods of biochemical analyses Vol. 16. Glick D, ed. New York: Interscience, 1968; 219-272 111 Hernandez HH, Chaikoff IL. Purification and properties of pancreatic cholesterol esterase. J Bioi Chem 1957; 228: 447-57 112 Sih CJ, Laval J, Rahim MA. Purification and properties of steroid esterase from Nocardia restrictus. J Bioi Chem 1963; 238: 566-71 113 Uwajima T, Tereda O. Purification and properties extracellular cholesterol ester hydrolase of Pseudomonas f1uorescens. Agricult Bioi Chem 1975; 39: 1511-12 114 Okawa Y, Yamaguchi T. Studies on sterol-ester hydrolase from Fusarium oxysporum. 1. Partial purification and properties. J Biochem (Tokyo) 1977; 81: 1209-15 115 Kamei T, Suzuki H, Matsuzaki M, Otani T, Kondo H, Nakamra S. Cholesterol esterase produced by Streptomyces lavendulae. Chem Pharm Bull 1977; 25: 3190-7 116 Roschlau P, Bernt E, Gruber W. Enzymatische Bestimmung des gesamt-Cholesterins im Serum. Z Klin Chem Klin Biochem 1974; 12: 403-7 117 Hyun J, Steinberg M, Treadwell CR, Vahouny GV. Cholesterol esterase-a polymeric enzyme. Biochem Biophys Res Commun 1971; 44: 819-25 118 Hyun J, Kothari H, Herm E, Mortenson J, Treadwell CR, Vahonny GV. Purification and properties of pancreatic juice cholesterol esterase. J Bioi Chem 1969; 244: 1937-45 119 Vahouny GV, Weersing S, Treadwell CR. Taurocholate protection of cholesterol esterase against proteolytic inactivation. Biochem Biophys Res Commun 1964; 15: 224-9 120 Kelly LA, Newman HAL Pancreatic sterol ester hydrolase: reversal of the reaction by bile salt. Biochim Biophys Acta 1971; 231: 558-60

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013

Analytical reviews in clinical biochemistry 121 Zoppi F, Fenili D. Enzymatic determination of total serum cholesterol with the Vickers D-300 analyzer. Clin Chem 1976; 22: 690-1 122 Siedel J, Hagele EO, Ziegenhorn J, Wahlefeld AW. Reagent for the enzymatic determination of serum total cholesterol with improved lipolytic efficiency. Clin Chem 1983; 29: 1075-80 123 Deacon AC, Dawson PJG. Enzymatic assay of total cholesterol involving chemical or enzymic hydrolysis: a comparison of methods. Clin Chem 1979; 25: 976-84 124 Noel SP, Dupras R, Filion AM. The activity of cholesterol ester hydrolase in the enzymatic determination of cholesterol: comparison of five enzymes obtained commercially. Anal Biochem 1983; 129: 464-71 125 Wiebe DA, Bernert JT. Influence of incomplete cholesterol ester hydrolysis on enzymic measurements of cholesterol. Clin Chem 1984; 30: 352-6 126 Demacker PNM, Boerma GJM, Baadenhuijsen H, Van Strik R, Leijnse B, Jansen AP. Evaluation of accuracy of 20 different test kits for the enzymic determination of cholesterol. Clin Chem 1983; 29: 1916-22 127 Burrin JM, Price CPo Measurement of blood glucose. Ann Clin Biochem 1985; 22: 327-42 128 Richmond W. Use of cholesterol oxidase for assay of total and free cholesterol in serum by continuous-flow analysis. Clin Chem 1976; 22: 157988 129 Allain CC, Poon LS, Chan CSG, Richmond W, Fu PC. Enzymatic determination of total serum cholesterol. Clin Chem 1974; 20: 470-5 130 Trinder P. Determination of glucose in blood using glucose oxidase with an alternative oxygen acceptor. Ann Clin Biochem 1969; 6: 24-7 131 Noma A, Nakayama K. Polarographic method for rapid microdetermination of cholesterol esterase and cholesterol oxidase. Clin Chem 1976; 22: 336-40 132 Roeschlau P, Bernt E, Gruber W. Cholesterol and esterified cholesterol 1974; 4: 1890. In: Methods of Enzymatic Analysis, Bergmeyer HU, ed. New York: Academic Press 133 Otomo M. The spectrophotometric determination of titanium with hydrogen peroxide and xylenol orange. Bull Chem Soc Japan 1963; 36: 1577-81 134 Tammes AR, Nordschow CD. An approach to specificity in glucose determinations. Am J Clin Pathol 1968; 49: 613-21 135 Papostathopoulos DS, Rechnitz GA. Enzymatic cholesterol determination using ion-selective membrane electrodes. Anal Chem 1975; 47: 1792-6 136 Harders HD, Helger R. Eine neue indikatorreaction fur die enzymatische cholesterinbestimmung. Lab Med 1977; 1: 141 137 Stahler F, Munz E, Kattermann R. Enzymatische Bestimmung von gesamt-Cholesterine im serum. Richfigkeit und Methodenvagleich. Dtsch Med Wochenschr 1975; 100: 876-80 138 Knob M, Rosenmund H. Enzymatische Bestimmung des Gesamtcholesterins im Serum mit Zentrifugalanalyzern. Z Klin Chem Klin Biochem 1975; 13: 493-8

595

139 Fruchart JC, Buassa-Bu-Tsumbu, Jaillard J, Sezille G. Automatisation en fluor imetrie du dosage enzymatique du cholesterol total serique. Clin Chim Acta 1975; 63: 399-402 140 Pesce MA, Bodourian SH. Enzymatic rate method for measuring cholesterol in serum. Clin Chem 1976; 22: 2042-5 141 Haeckel R, Perlick M. A new enzymatic determination of cholesterol. II. The use of aldehyde dehydrogenase to measure h202 producing reactions. J Clin Chem Clin Biochem 1976; 14: 411-14 142 Huang H, Jui-Chang WK, Guilbault CG. Fluorimetric enzymatic determination of total cholesterol in serum. Clin Chem 1975; 21: 1605-8 143 Deeg R, Ziegenhorn J. Kinetic enzymic method for automated determination of total cholesterol in serum. Clin Chem 1983; 29: 1798-802 144 Cary PL, Johnson CA, Whitter PD, Parker JW. Evaluation and comparison of a radiative energy attenuation method for determining cholesterol in serum. Clin Chem 1985; 31: 605-8 145 Stahler F. The technology of dry versus wet chemistry. 1986: 10-20. In: Clinical Biochemistry: Nearer the Patient, Vol. 2. Marks V, Alberti KGMM, eds. London: Bailliere Tindall 146 Steinhausen RL, Price CP. Principles and practice of dry chemistry systems. In: Recent Advances in Clinical Biochemistry, III. Marks V, Alberti KGMM, eds. London: Churchill Livingstone, 1985, 273-91 147 Nelson LM, Clark RS, Fraser CG. A laboratory and in-ward evaluation of cholesterol assays on the Ames Seralyzer. J Automatic Chem 1985; 7: 173-6 148 Shepherd J, Packard CJ, Anggard EE, Land JM, Lenihan CJ, Percy MJ, Ritchie LD. Practical coronary prevention: the impact of drug chemistry analysers, In: Clinical Biochemistry: Nearer the Patient, Vol. 2. Marks V, Alberti KGMM, eds. Bailliere Tindall. 1986; 142-7 149 von Schenck H, Treichi L, Tilling B, Olsson AG. Laboratory and field evaluation of three desktop instruments for assay of cholesterol and triglycerides. Clin Chem 1987; 33: 1230-2 ISO Orrel JM, Pettigrew AR, Dominiczak MH. Longterm performance of an extra-laboratory analyser in a lipid out-patient clinic. Ann Clin Biochem Supp! 1988; 25: 229-30 151 White DL, Brown LF, Feld RD. Effects of bilirubin on detection of hydrogen peroxide by use of peroxidase. Clin Chem 1978; 24: 1778-82 152 Pesce MA, Bodourian SH. Enzymic measurement of cholesterol in serum with the Centrifichem centrifugal analyser. Clin Chem 1977; 23: 280-2 153 Fossati P, Prencipe L, Berti G. Use of 3,5dichloro-2-hydroxy-benzenesulfonic acid!4-aminophenazone chromogenic system in direct assay of uric in serum and urine. Clin Chem 1980; 26: 228-31 154 Spain MA, Wu AHB. Bilirubin interference with determination of uric acid, cholesterol, and triglycerides in commercial peroxidase-coupled assays, and the effect of ferrocyanide. Clin Chem 1986; 32: 518-21

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013

596

Richmond

155 Artiss JD, McEnroe RJ, Zak B. Bilirubin interference in a peroxidase-coupled procedure for creatinine elimination by bilirubin oxidase. Clin Chem 1984; 30: 1389-92 156 Maguire GA, Bannister MW. The "chromogen oxidase" activity of bilirubin oxidase. Clin Chem 1987; 33: 1304 157 Fossati P, Prencipe L. La reazione di EmersonTrinder: studio dei vari crornogeni principali interferenze. Quad Sclavo Diagn 1978; 14: 164-77 158 Kroll MH, Lindsey H, Greene J, Silva C, Hainline A, Ellin RJ. Bias between enzymatic methods and the reference method for cholesterol. Clin Chem 1988; 34: 131-5 159 US Department of Health and Human Services. Reportfrom the Laboratory Standardisation Panel of the National Cholesterol Education Programme. NIH Publication No. 90-2964, 1990 160 Gilbert RK. Accuracy of clinical laboratories measured by comparison with definitive methods. Am J Clin Pathol 1978; 70: 450-67 161 HartmannAE, Naito HK, Burnett RW, Welch MJ. Accuracy of participant results utilised as target values in the CAP chemistry survey programme. Arch Pathol Lab Med 1985; 109: 894-903 162 Warnick G, Mayfield C, Albers J. Evaluation of quality-control materials for high density lipoprotein cholesterol of quantitation. Clin Chem 1981; 27: 116-23 163 Kannel WB, Castelli W, Gordon T, et al. Serum cholesterol, lipoprotein, and risk of coronary heart disease: The Framingham Study. Ann Intern Med 1971; 74: 1-12 164 Anon. Relationship of blood pressure, serum cholesterol, smoking habit, relative weight, and ECG abnormalities of incidence of major coronary events: Final report of the Pooling Project Research Group. J Chronic Dis 1978; 31: 201-306 165 Goldbourt V, Holtzman E, Neufeld HN. Total and high density lipo-protein cholesterol in the serum and risk of mortality. Evidence of a threshold effect. BMJ 1985; 290: 1239-43 166 Martin MJ, Hulley SB, Browner WS, Kuller LH, Wentworth D. Serum cholesterol, blood pressure, and mortality: implications from a cohort of 361,662 men. Lancet 1986; ii: 933-6 167 Stamler J , Wentworth D, Neaton J. Is the relationship between cholesterol and risk of death from coronary heart disease continuous and graded? JAm Med Assoc 1986; 256: 2823-28 168 Rose G, Shipley M. Plasma cholesterol concentration and death from coronary heart disease: 10 year results of the Whitehall study. BMJ 1986; 293: 306-7 169 Hjerrnann I, Holme I, Velve Byre E, et al. Effect of diet and smoking intervention on the incidence of coronary heart disease. Report from Oslo Study Group of a randornised trial of healthy men. Lancet 1981; II: 1303-10 170 Blankehorn DH, Nessim SA, Johnson RL, et al. Beneficial effects of combined colestipol-niacin therapy on coronary venous bypass grafts. JAm Med Assoc 1987; 257: 3233-40

171 The Expert Panel. Report of the National Cholesterol Education Program expert panel on detection, evaluation, and treatment of high blood cholesterol in adults. Arch Intem Med 1988;148: 36-69 172 Study Group of the European Atherosclerosis Society. Strategies for the prevention of coronary heart disease: a policy statement of the European Atherosclerosis Society. Eur Heart J 1987; 8: 77-88 173 Shepherd J, Betteridge DJ, Durrington P, et al. Strategies for reducing coronary heart disease and desirable limits for blood lipid concentrations: Guidelines of the British Hyperlipidaemia Association. BMJ 1987; 295: 1245-6 174 Laboratory Standardisation Panel. Current status of blood cholesterol measurement in clinical laboratories in the United States: A report from the Laboratory Standardisation Panel of the National Cholesterol Education Programme. Clin Chem 1988; 34: 193-201 175 Broughton PMG, Buckley BM. The need for better plasma cholesterol assays. Ann Clin Biochem 1985; 22: 547-9 176 Halinline A, Hill P, Garbaczewski L, Winn C. Quality control of lipid measurements in epidemiological studies: the US Air Force Program. Clin Chem 1985; 31: 261-3 177 Statland BE. Laboratory management, quality assurance and references values. Clin Biochem Rev 1%9; 3: 1-28 178 Harris EK. Statistical principles underlying analytic goal-setting in clinical chemistry. Am J Clin Pathol 1979; 72: 374-82 179 World Association of Societies of Pathology: Proceedings of the Subcommittee on Analytical goals in clinical chemistry: Their relationship to medical care. Am J Clin Patho11979; 7: 624-30 180 Fraser CG. The application of theoretical goals based on biological variation data in proficiency testing. Arch Pathol Lab Med 1988; 112: 404-15 181 Rotterdam EP, Katan MB, Knulman JT. Importance of the time interval between repeated measurements of total or high-density lipoprotein cholesterol when estimating an individuals baseline concentrations. Clin Chem 1987; 33: 1913-15 182 Whitby IG. Medical implications of quality control in clinical biochemistry. Ann Clin Biochem 1969; 6: 104-8 183 Kannel EB. Cholesterol and risk of coronary heart disease and mortality in men. Clin Chem 1988; 34/8: B53-59 (Suppl.) 184 Warnick GR, Cheung MC, Albers 11. Comparison of current methods for high-density lipoprotein cholesterol quantitation. Clin Chem 1979; 25: 596-604 185 Demacker PNM, Vos-Janssen HE, Hijmans AGM, Van't Laar A, Jansen AP. Measurement of highdensity lipoprotein cholesterol in serum: Comparison of six isolation methods combined with enzymic cholesterol analysis. Clin Chem 1980; 26: 1780-6 186 Warnick GR, Benderson J, Albers 11. Dextran sulphate-Mg'" precipitation procedure for quantitation of high-density-lipoprotein cholesterol. Clin Chem 1982; 28: 1379-88

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013

Analytical reviews in clinical biochemistry 187 Wiebe DA, Smith Sl. Six methods for isolating high-density lipoprotein compared, with use for the reference method for quantifying cholesterol in serum. Clin Chern 1985; 31: 746-50 188 Warnick GR, Nguyen T, Albers AA. Comparison of improved precipitation procedures for quantitation of high-density lipoprotein cholesterol. Clin Chern 1985; 31: 217-22 189 Demacker PNM. Accuracy and precipitation efficiency of improved precipitation methods for quantifying high-density-lipoprotein cholesterol. Clin Chern 1985; 31: 1768-70 190 Gidez LI, Miller or, Burstein M, Slagle S, Eder HA. Separation and quantitation of subclasses of human plasma high density lipoproteins by a simple precipitation procedure. J Lipid Res 1982; 23: 1206-23 191 Warnick GR, Henderson 1M, Albers 11. Quantitation of high-density-lipoprotein subclasses after separation by dextran sulphate and Mg2+ precipitation. Clin Chern 1982; 28: 1574 192 Talameh Y, Wei R, Naito H. Measurement of total HDL, HDL2 and HDLJ by dextran sulphateMgCI2 precipitation technique in human serum. Clin Chim Acta 1986; 158: 33-41 193 Kosnter GM, Molinari E, Pichler P. Evaluation of a new HDL2IHDLJ quantitation method based on precipitation with polyethylene glycol. Clin Chim Acta 1985; 148: 139-47 194 Friedwald WT, Levy RI, Fredrickson DS. Estimation for the concentration of low-density lipoprotein cholesterol in plasma, without the use of the preparative ultracentrifuge. Clin Chern 1972; 18: 448-502 195 Assmann G, Hu 1, Kohnert U, et 01. LDLcholesterol in blood serum following precipitation of LDL with polyvinyl sulphate. Clin Chim Acta 1984; 140: 77-83 196 Wieland H, Seidel D. A simple specific method for precipitation of low density lipoproteins. J Lipid Res 1983; 24: 904-9 197 Hoffman GE, Hiefinger R, Weiss L, Poppe W. Five methods for measuring low-density lipoprotein cholesterol in serum compared. Clin Chern 1985; 31: 1729-30 198 Demacker PN, Hijmans AG, Brenninkmeijer Bl, lansen AP, van't Laar A. Five methods for determining low-density lipoprotein cholesterol compared. Clin Chern 1984; 30: 1797-800 199 DeLong DM, DeLong ER, Wood PD, Lippel K, Rifkind BM. A comparison of methods for the estimation of plasma low- and very low-density lipoprotein cholesterol. J Arn Med Assoc 1986;256: 2372-7 200 Niedbala RS, Schray Kl, Foery R, Clement G. Estimation of low-density lipoprotein by the

201 202 203 204

205

206

207

208

209 210 211

212 213

214

597

Friedwald formula and by electrophoresis compared (Letter). Clin Chern 1985; 31: 1762-3 Lipi U, Graziani MS, Manzato F, Schinella M. The Friedwald formula: Statistical acrobatics? (Letter and reply). Clin Chern 1986; 32: 909-11 Kazi-Aoul T, Benmiloud M. The Friedewald formula: another restriction? Clin Chern 1987; 33: 1302 Ford RP. Essential data derived from biological variation for establishment and use of lipid analyses. Ann Clin Biochem 1989; 26: 281-5 Gibson lC, Rubinstein A, Brown WV. Precipitation of apo E-containing lipoproteins by precipitation reagents for apolipoprotein B. Clin Chern 1984; 30: 1784-8 Simpson HS, Ballantyne FC, Packard Cl, Morgan GM, Shepherd 1. High-density lipoprotein subfraction as measured by differential polyanionic precipitation and rate zonal ultracentrifugation. Clin Chern 1982; 28: 2040-3 Demacker PNM, Hak-Lemmers HLM, Hijmans AGM, Baadenhusen H. Evaluation of the dualprecipitation method for determination of cholesterol in high-density lipoprotein subfractions HDL2 and HDLJ in serum. Clin Chern 1986; 32: 819-25 Steele BW, Koehler DF, Azar MM, Blaszkowski TP, Kuba K, Dempsey ME. Enzymatic determination of cholesterol in high-density-lipoprotein fractions by a precipitation technique. Clin Chern 1976; 22: 98-101 Henderson LO, Lagarde E, Herbert PN. Artifactual reduction of high-density lipoprotein cholesterol estimates after dextran sulphate-Mg2 + precipitation. Arn J Clin Pathol 1980; 73: 664-8 Torrens Dl, Feher MD, Richmond W. Interference of EDT A with HDL subfraction determination. Ann Clin Biochem 1988; 25: 227-8 Bush TL, Fried LP, Barrett-Connor E. Cholesterol, lipoproteins, and coronary heart disease in women. Clin Chern 1988; 34/8: B6O-70 (Suppl.) Gordon T, Castelli WP, Hjortland MC, Kannel WB, Dawber TR, High density lipoprotein as a protective factor against coronary heart disease. Arn J Med 1977; 62: 707-14 Bachorik PS. Collection of blood samples for lipoprotein analysis. Clin Chern 1982; 28: 1375-8 Ungaro B, Corso G, Delio Russo A. Cholesterol concentrations in serum-plasma pairs differs because of water shift from blood cells. Clin Chern 1985; 31: 1096-7 Stokes YM, Salmond CE, Carpenter LM, Welby T1. Stability of total cholesterol, high-densitylipoprotein cholesterol, and triglycerides in frozen sera. Clin Chern 1986; 32: 995-9

Accepted for publication 18 February 1992

Downloaded from acb.sagepub.com at EBSCO Electronic Journals Service (EJS) on November 20, 2013