Postgraduate Medicine
ISSN: 0032-5481 (Print) 1941-9260 (Online) Journal homepage: http://www.tandfonline.com/loi/ipgm20
Red cell indexes revisited: Review with test cases Patrick C. J. Ward To cite this article: Patrick C. J. Ward (1979) Red cell indexes revisited: Review with test cases, Postgraduate Medicine, 65:5, 282-289, DOI: 10.1080/00325481.1979.11715158 To link to this article: http://dx.doi.org/10.1080/00325481.1979.11715158
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LABORATORY MEDICINE A Series
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Red cell indexes revisited: Review with test cases This, the Iast in the group of articles on laboratory investigation of anemia, reviews the red cell indexes and their significance in diagnosis and then presents brief test cases for readers to assess their knowledge. In each test case, indexes and blood smear form the basis for investigative strategy and conclusions.
Patrick C. J. Ward, MD
In the preceding articles in this series on laboratory investigation of anemia (January through April issues), the importance of red cell indexes in the early workup of anemia was amply stressed. Increased reliance on indexes over the past two decades stems from the widespread availability of automated electronic particie counters, which confer on these measurements a degree of accuracy not hitherto attainable. Most of the world literature on indexes since the advent of these deviees derives from data generated by the Coulter Counter Mode! S.* This counter, which is available in 80% of hospitals in the United States with 300 beds or more, 1 has added a new dimension of accuracy to both the red cell count and mean corpuscular volume (MCV). Indexes Red cel/ count-Before the 1960s, the graduai decline in reliance on indexes reflected the imprecision of the red cell count as measured in the hemocytometer counting chamber. The coefficient of variation was be•cou! ter Electronics, !ne. H ialeah. Florida.
282
tween 5.5% and 9.0% or even higher when the count was very low.2 Furthermore, chamber counts consistently overestimated cell numbers.3 With the advent of particle counters, not only were precision and accuracy sharply increased but the count was found to be lower than hitherto suspected. The coefficient of variation feil to between 1% and 2%. Mean corpuscular volume-Because of the imprecision of the red
One of a series of articles on orderlng and lnterpretlng laboratory tests whlch began ln April1978
cell count as measured in the hemocytometer chamber, the derived MCV (hematocrit [Hct]jred cell count [RBC]) was also imprecise. Furthermore, the normal range (87±5 cu J..L) was too low. With the advent of the particle counter, the lowered red cell count brought about an expansion of the upper end of the normal range of the MCV to 97 cu J..L. (Actually, 100 cu J..L is more commonly used as the cutoff point in clinicat practice.) In the Coulter S, the MCV is calculated directly. As each RBC passes through an electronic sensor, it generates an impulse and a change in electrical resistance proportional to its volume. The cumulative resistance divided by the number of impulses is translated into the MCV. Despite the fact that the Coulter S slightly overestimates the MCV, particularly in the low range,4 the data generated are considered adequate for clinicat purposes and an enormous improvement over the MCV calculated from the centrifuged hematocrit value and the hemocytometer red cell count (Hctf RBC). Hemog/obin-Hemoglobin levels as measured by standard and Coulter methods are identical and therefore warrant no further corn-
VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
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ment. Hematocrit-Even in normal blood, the hematocrit value measured by centrifugation slightly overestimates the true packed red cell volume because of plasma trapped between the cells. This minor overestimation (3%) is of little clinical significance when RBCs are normal in size and shape. However, plasma trapping may account for 20% or more of the packed red cell column (centrifuged hematocrit) in the presence of marked poikilocytosis, notably in sickle cell anemia. 5 To a lesser extent, this is also true of hypochromic states,s possibly on the basis of the associated poikilocytosis. The clinical implications are obvious. In the Coulter S, the hematocrit is not measured by centrifugation but rather calculated from the formula Hct = MCV x RBC. (This is merely a restatement of the basic calculation MCV = Hct/ RBC.) In determining the MCV, however, the Coulter S does not take poikilocytosis into account. It is sensitive to changes in volume only and is insensitive to changes in shape. Hence, the problem of plasma trapping no longer obtains. In normal individuals, the calculated hematocrit is 1.5% Jess than the centrifuged hematocriP In the presence of marked poikilocytosis, erroneous conclusions may be drawn if the physician switches from one method of measuring the hematocrit to the other in following the patient.
VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
Mean corpuscular hemoglobin (MCH)-Although sorne authors have recently espoused a low MCH as a sensitive measure of iron deficiency, 6 others have pointed out that since the MCH varies linearly with the MCV, it adds little in this situation. 7 With the improved accuracy of the red cell count, the MCH, like the MCV, has become respectable, although redundant. Mean corpuscular hemoglobin concentration (MCHC)- The MCHC was originally designed to reflect incipient hypochromasia, ie, decreased weight per unit volume (Hgb~/ Hct) in patients with evolving iron deficiency. In this function, it performed relatively weil. With the advent of electronic particle counters, however, the MCHC was found to be insensitive to ali but severe degrees of hypochromasia-for a curious reason. 8 In evolving iron deficiency, a degree of poikilocytosis is always present. Hence, because of the associated plasma trapping, the centrifuged hematocrit is spuriously high. Although the falling MCHC of evolving hypochromasia should primarily reflect a disproportionate fall in hemoglobin in relation to hematocrit, the effect is exaggerated by Patrick C. J. Ward Dr Ward is director of clinical laboratories. Mount Sinai Hospital, and associate professor of laboratory medicine and pathology, University of Minnesota Medical School. Minneapolis.
the simultaneously (but spuriously) increased hematocrit. The low MCHC of iron deficiency now equals Hgb~ 1Hctt rather than Hg~ 1Hct. Hence, an MCHC derived from a centrifuged hematocrit reflects both hypochromasia and poikilocytosis, the latter contributing significantly to the sensitivity of this measurement in detecting the mild hypochromasia of early iron deficiency. In the Coulter S method, the role of poikilocytosis in determination of the MCHC has been elimïnated, since the hematocrit is calculated rather than measured by centrifugation and therefore no plasma trapping is present. Hence, a factor (admittedly spurious) has been eliminated and the calculated MCHC is no longer as sensitive in detecting mild degrees of hypochromasia, such as might be anticipated in early iron deficiency. 8 The MCHC does fall in advanced iron deficiency, but the problem remains that hypochromasia may be visible on smears while the MCHC is normal. At the other end of the scale and by both methods, the MCHC may be effective in detecting sorne cases of congenital spherocytic anemia. When the MCHC is 36% or more and both hypertriglyceridemia and cold agglutinin disease have been excluded,9,IO the patient has congenital spherocytic anemia. The absence of such increases, however, does not exclude this disease. continued
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LABORATORY MEDICINE CONTINUED
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With the advent of electronic particle counters, the precision and accuracy of the red cell count and MCV have increased considerably.
Diagnostic exercise The following brief test cases are based on the investigative process described in the preceding articles in this series on anemia. The final diagnosis is provided in each case. For reference, the normal ranges for red cell indexes suggested by Coulter Electronics, Inc, are given in table 1. Table 1. Nonnal values for red cell indexes• Index
Nonnal values
Males
Females
5.4±0.7 4.8±0.6 Red cell count (RBC) (x10"/cu mm) Hemoglobin (Hgb) (gm/dl)
16.0±2
14.0±2
Hematocrit (Hct)
47±5
42±5
87±7
90±9
Mean corpuscular hemoglobin (MCH) (pg)
29±2
29±2
Mean corpuscular hemoglobin concentration (MCHC)
34±2
34±2
Case 1 35-year-old black female with neckinjury. Routine admission Coulter S panel: RBC 4.77 Hgb 12.6 Hct 37.8 MCV 79 MCH 26.4 MCHC 33.1 Discussion The panel shows a very minor degree of microcytosis. There is no anemia. The discriminant function (DF') is positive. The smear is normal, ie, microcytosis of the degree present by MCV would be impossible to detect visually.
(%)
Mean corpuscular volume (MCV)
Case2 76-year-old white female with a long history of rheumatoid arthritis. Taking indomethacin and aspirin intermittently. Coulter S panel: RBC 3.96 Hgb 6.7 Hct 24 MCV 61 MCH 17.1 MCHC 27.4 Discussion The panel shows severe hypochromic microcytic anemia. The history atone is consistent with iron deficiency anemia (perhaps from drug-induced gastric bleeding), the anemia of chronic disease, or both. The DF' is positive. The MCV strongly suggests iron deficiency anemia, since the MCV of the anemia of chronic disease rarely falls below 72 cu J.l..u Nevertheless, an element of anemia of chronic disease cannot be ruled out.
(CU p.)
Investigation Serum iron (30 }.l.g/ dl), serum ironbinding capacity (474 p.gf dl).
(%)
*Coulter Counter Model S.
Conclusion Iron deficiency state without anemia. Further history of very heavy menses elicited.
Investigation Serum iron ( 15}.1.g/ dl), serum iron-binding capacity (178 J.l.g/dl), guaiac test (negative), upper gastrointestinal series (normal). Conclusion Not currently bleeding. Although the iron data are more consistent with anemia of chronic disease, there is quite probably an element of iron deficiency. Iron therapy started with a view to reversing the anemia to the extent that iron deficiency is causative. 11
284
VOL 65/NO 5/MAY 1979/POSTGAADUATE MEDICINE
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The hematocrit value determined by the centrifugation method slightly overestimates the packed red cell volume because of plasma trapping between ce lis. This error is compounded when poikilocytosis is present.
Case 3 72-year-old white female with long history of hematologie disorder. Hepatosplenomegaly. Coulter S panel:
Case4 31-year-old white male with four-year his tory of buming sensations and tingling in both feet. Coulter S panel:
RBC 6.26 Hgb 15.0 Hct 48.2 MCV 77 MCH 24.0 MCHC 31.4
RBC 4.14 Hgb 15.7 Hct 47.2 MCV 113 MCH 37.8 MCHC 32.8
Discussion The indexes show mild microcytosis, marginal hypochromasia, and erythrocytosis. The DF'isnegative. In the absence of hepatosplenomegaly, these data would ordinarily suggest thalassemia mi nor. The smear shows teardrop poikilocytosis. Hypochromasia not shown.
Discussion These data reveal macrocytosis without anemia. Patients presenting with macrocytosis but without anemia have been described as candidate occult alcoholics.u In the absence of vitamin 8 12 or folate deficiency, such macrocytosis may be the consequence of a direct effect of alcohol on the developing erythroblast 14 and precede anemia.
Investigation Serum iron (44 J.Lg/ dl), serum ironbinding capacity (380 J.Lg/ dl), hemoglobin electrophoresis (normal). Conclusions Polycythemia vera with mild iron deficiency. The indexes in polycythemia vera with iron deficiency anemia may simula te those of thalassemia minor. 12 The mild erythrocytosis and negative DF' are common to both disorders. The teardrop forms reflect splenomegaly and suggest a degree of evolving (secondary) myelofibrosis, ie, the "spent" phase of polycythemia vera.
VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
Case 5 50-year-old obese plethoric white male noted to have increased blood pressure on routine physical examination. Coulter S panel: RBC 6.62 Hgb 21.4 Hct 63.8 MCV 97 MCH 32.3 MCHC 33.4 Discussion These data reflect a polycythemic state. The smear shows a uniform cell.population. The MCV is at the upper limit of normal, a leve! usually encountered in the later decades of life. 15 In the presence of polycythemia, neither vitamin 8 12 nor folate deficiency merits serious consideration. It has been noted thatthe MCVtends to be increased by smoking, chronic hypoxia, and chronic carbon monoxide poisoning. 15 Any of these may be causally related to a polycythemic state.
Investigation Reticulocyte count (normal); serum vitamin 8 1", serum and red cell folates (normal); liver function tests (mildly abnormal). Conclusions The uniform macrocytosis in the smear in conjunction with the other test results favors liver disease. Long history of alcoholism finally elicited from the patient. Final diagnosis: alcoholic polyneuropathy.
Investigation Carboxyhemoglobin leve! (17% and 12% on two occasions). Conclusions History of smoking between 12 and 20 cigars a day elicited. Final diagnosis: smokers' polycythemia. 16 Hypertension felt to be unrelated.
continued
285
SLO.PHYLLIN-t GYROCAPS;J 60 mg., 125 mg., 250 mg. (theophylline, anhydrous) SLO.PHYLLIN® TABLETS 100 mg. and 200 mg. (theophylline, anhydrous)
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SLO.PHYLLINJr 80 SYRUP (theophylline, anhydrous) Composition: Slo-Phyllin"' Gyrocaps® (timed release capsules) contain Theophylline (anhydrous) in a special base !hat provides for a prolonged therapeutic affect. Each Slo-Phyllin-' 60 {white color, dye-free) Gyrocap~ contains 60 mg. of Theophylline (anhydrous). Each Slo-Phyllin-~ 125 (brown color) Gyrocap-~ contains 125 mg. of Theophylline (anhydrous). Each Slo-Phyllin' 250 (purple color) Gyrocap! contains 250 mg. of Theophylline (anhydrous). Slo-Phyllin"' tablets {white, scored, dye-free) contain prompt acting Theophylline in two strengths. Slo-Phyllm' 100 mg. tablet and Slo-Phyllin~ 200 mg. tablet. Slo-Phyllin·' 80 Syrup (orange color. nonalcoholic) contams 80 mg. of Theophylline (anhydrous) per 15 ml. (one tablespoonful). Indications: Slo-Phyllin •• is used in the trealment of asthma and other pulmonary disorders in which a reversible bronchoconstrictive element may be present such as chronic bronchitis and emphysema. Side EHects: Theophylline may cause gastric irritation, nausea, vomittng, and abdominal discomfort, headache, palpitation, !ali in blood pressure, central nervous system stimulation, and diuresis. Slo-Phyllin~ Gyrocaps .. are formulated in a timed release form to minimize these gastric complatnts. Precautions: Slo-Phyllin" should not be used concurrently with other formulas containing xanthine derivatives. Warnlng: Safety in human pregnancy has not been established Dosage and Administration: Slo-Phyllin"" Gyrocaps~ 60 mg.-125mg. -250mg. CHILDREN UNDER 12: The recommended dosage range is 3-5 mg./kg body weight every 8 hours. An initial dosage of 4 mg./kg. body weight every 8 hours to a maximum of 16 mg./kg./24 hours is recommended. If the dosage is to be increased, it should be done in small increments up to a maximum of 24 mg./kg./24 hours or 900 mg./24 hours whichever is less. If the patient is to be maintained at a near maximum of the recommended dosage levels, serum theophylline levels should be determined. ln children, not more than 8 mg./kg. every 8 hours should ordinarily be given. If side affects should occur, the dosage should be reduced by 1 mg./kg./dose. ADULTS AND CHILDREN OVER 12: An initial dosage of 4 mg./kg. body weight every 8 hours is recommended. The recommended median dose is 8 mg./kg. every 8 hours. This dosage can be approached by increasing the initial dose by increments of 60 mg. to 125 mg. at 3 to 4 day intervals as long as adverse affects are not achieved. Because of the risk of reaching taxie serum theophylline levels (above 20 ,..g.lml.), serum theophylline concentrations should be obtained il higher doses are to be maintained.
The average adult dose is 930 mg./24 hours. However, sorne individuals may require doses as htgh as 2000 mg./24 hours. For greater flexibility and easier titration of dosage. Slo-Phyllin~· Gyrocaps·"' are available in 3 dosages-60 mg, 125 mg., and 250 mg. These dosages may be used interchangeably or complementary to one another in arder to achieve the desired dosage level. Slo-Phyllin-' Tablets and Slo-Phyllin~ 80 Sy!.l.!f,l Theophyllinize (titrate) each patient using Slo-Phyllin® at the recommended dosage of 3-5 mg./kg. body weight every six hours. lnitially the lower dosage should be administered, then the dosage may be increased if optimal bronchodilator affects are not achieved. lt is generally advised thal a dosage of 5 mg./kg. body weight every six hours not be exceeded unless it is possible to monitor serum theophylline concentrations during therapy si nee it has been establtshed that signtficant variations occur among individuals in the rate at which the drug is eliminated from the body Recommended Dosage of SLO.PHYLLIN"' Tablets tor Various Body Welghts
1 Weight lbs.
Dose (in mg)
1
3 mg/kg 4 mg/kg 5 mg/kg 6 mg/kg
kg
22 10 33 15 44 20 55 25 66 30 88 40 110 50 132 60 154 70 176 80 198 90 220 100
30 45 60 75 90 120 150 180 210 240 270 300
40 60 80 100 120 160 200 240 280 320 360 400
50 75 100 125 150 200 250 300 350 400 450 500
60 90 120 150 180 240 300 360 420 480 540 600
Administered every six hours. Recommended Dosage of SLO.PHYLLIN"' 80 Syrup for Varlous Body Weights
f Weight
Dose (in tsp.)
lbs.
kg
3 mg/kg
20 40 60 79
9 18 27 36
1 tsp. 2 tsp. .3 tsp. 4 tsp.
5 mg/kg
1 VJ tsp.
1V2 tsp. 3 tsp. 5 tsp. 6V2 tsp.
4 tsp . 5 tsp.
CONTINUED
Case6 42-year-old white female undergoing preemployment physical examination in hospital. Coulter S panel: RBC 3.92
Hgb 13.5 Hct 36.8 MCV 94 MCH 34.4 MCHC 36.5 Discussion Aside from the slightly low red cell count (which is difficult to explain except perhaps on the basis of lysis of sorne ce lis during the Coulter S dilution process), the single finding demanding attention is the increased MCHC. The patient is not anemie, ie, hemoglobin is 13.5 gmfdl.
1
4 mg/kg
2v2 tsp.
LABOAATOAY MEDICINE
Administered every six hours. The therapeutic serum theophylline concentration is considered to be between 10 and 20 ,..g.tml. This range may best be reached by individualizing the patient's dosage while concomitantly monitoring the serum theophylline concentrations. Slo-PhyllinJr 80 Syrup U.S. Patent #3928609 How Supplied: Slo-Phyllin® Gyrocaps"'-Bottles of 100 and 1000 unit dose pkgs. (125 mg. and 250 mg. only) Syrup-Pints and gallons unit dose botties, 5 ml. and 15 ml. Tablets-Bottles of 100 and 1000 unit dose pkgs.
Innstigation Osmotic fragility (increased). Conclusion Even without the smear, these data are collectively diagnostic of congenital spherocytosis. (Actually, the increased MC H C per se is virtually diagnostic of this disease; the increased osmotic fragility merely supports the diagnosis.)
-DDDNER 1!!1
LABDRATDRIEB, INC.
Subsidiary of: William H. Rorer, lnc. Fort Washington, PA 19034 VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
For detecting hypochromasia, the MCHC determined by electronic partie le counters is less sensitive than that determined by older methods.
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Case 7 60-year-old female with myxedema and diabetes. Coulter S panel: RBC 3.89 Hgb 17.4 Hct 34.6 MCV 88 MCH 42.1 MCHC 47.3 Discussion These data are unacceptable, since the normal ratio of roughly 3: 1 between hematocrit and hemoglobin does not obtain. One or the other test result is spurious. In this context, therefore, the high MCHC (Hgb/ Hct) is invalid (although arithmetically correct). The diagnostic possibilities are therefore hypertriglyceridemia and cold agglutinin disease rather than congenital spherocytic anemia.
hemoglobin determination by causing turbidity in the red celllysate. The derived indexes (MCH and MCHC) are therefore also rendered spurious. The correct indexes may be obtained by resuspending the RBCs in physiologie saline solution. 9 More simply, a reasonable approximation ofthe true hemoglobin value may be derived by dividing the hematocrit by 3. (lt should be understood that the hematocrit value is valid, since it derives from two measurements unaffected by hyperlipidemia, ie, red cell count and MCV.) Next month: A practical approach to diagnosis of infectious mononucleosis. Series coordinator: M. Desmond Burke, MD, associate pathologist, Mount Sinai Hospital, and associate professor of laboratory medicine and pathology, University of Minnesota Medical School, Minneapolis. Address reprint requests to Patrick C. J. Ward. MD. Mount Sinai Hospital, 2215 Park Ave, Minneapolis, MN 55404.
Investigation Cold agglutinin test (negative; further, RBCs normal in smears, with no evidence of autoagglutination in smears prepared at room temperature). Blood lipid studies: cholesterol (600 mg/ dl), triglycerides (12,600 mg/dl). Serum markedly hyperlipemic. Conclusion Hyperlipidemia superimposed on very mild normochromic normocytic anemia. Recent data suggest that hyperchylomicronemia rather than hypertriglyceridemia is responsible for aberrent indexes of this type. 9 Chylomicrons interfere with
VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
References l. Cunningham LO, Rising JA: Erythrocytic microcytosis: Clinical implications in 100 patients. Am J Med Sei 273:149-155, 1977 2. Hattersley PG: Macrocytosis of the erythrocytes: A preliminary report. JAMA 189: 997-999, 1964 3. HamiHon PJ, Davidson RL: The interrelationships and stability of Coulter S-determined blood indices. J Clin Pathol 26:700705, 1973 4. England JM, Down MC: Measurement of the mean cell volume using electronic particle counters. Br J Haematol 32:403409, 1976 5. England JM et al: Re-assessment of the reliability of the hematocrit. Br J Haematol 23:247-256, 1972 6. Griner PF, Oranburg PR: Predictive values of erythrocyte indices for tests of iron, folie acid and vitamin B, deficiency. Am J Clin Pathol 70:748-752, 1978 7. Croft RF et al: Red cell indices in megaloblastosis and iron deficiency. Pathology 6:107-117, 1974 8. Rose MS: Epitaph for the MCHC. Br Med J 2:169, 1971 9. Gagne C et al: Effect of hyperchylomicronemia on the mea~urement of hemoglobin. Am J Clin Pathol68:584-586, 1977 10. Hattersley PG et al: Erroneous values on the Mode! S Coulter Counter due to high liter cold agglutinins. Am J Clin Pathol 55:442446, 1971 11. Cartwright GE, Lee GR: The anemia of chron!c disorders. Br J Haematol21:147-152, 1971 12. Hamblin TJ: Differentiation of iron deficiency from thalassemia trait by routine blood-count. (Letter) Lance! 1:676, 1973 13. Unger KW, Johnson D Jr: Red blood cell mean corpuscular volume: A potential indicator of alcohol usage in a working population. Am J Med Sei 267:2tll-2tl9, 1974 14. Wu A et al: Macrocytosis of chronic alcoholism. Lance! 1:tl29-831, 1974 15. Okuno T: Red cell size as measured by the Coulter Mode! S. J Clin Pathol 25:599.{)02, 1972 16. Smith JR, Landaw SA: Smokers' polycythemia. N Engl J Med 298:6-10, 1978
289
ISSN: 0032-5481 (Print) 1941-9260 (Online) Journal homepage: http://www.tandfonline.com/loi/ipgm20
Red cell indexes revisited: Review with test cases Patrick C. J. Ward To cite this article: Patrick C. J. Ward (1979) Red cell indexes revisited: Review with test cases, Postgraduate Medicine, 65:5, 282-289, DOI: 10.1080/00325481.1979.11715158 To link to this article: http://dx.doi.org/10.1080/00325481.1979.11715158
Published online: 07 Jul 2016.
Submit your article to this journal
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ipgm20 Download by: [Australian Catholic University]
Date: 19 August 2017, At: 09:46
LABORATORY MEDICINE A Series
Downloaded by [Australian Catholic University] at 09:46 19 August 2017
Red cell indexes revisited: Review with test cases This, the Iast in the group of articles on laboratory investigation of anemia, reviews the red cell indexes and their significance in diagnosis and then presents brief test cases for readers to assess their knowledge. In each test case, indexes and blood smear form the basis for investigative strategy and conclusions.
Patrick C. J. Ward, MD
In the preceding articles in this series on laboratory investigation of anemia (January through April issues), the importance of red cell indexes in the early workup of anemia was amply stressed. Increased reliance on indexes over the past two decades stems from the widespread availability of automated electronic particie counters, which confer on these measurements a degree of accuracy not hitherto attainable. Most of the world literature on indexes since the advent of these deviees derives from data generated by the Coulter Counter Mode! S.* This counter, which is available in 80% of hospitals in the United States with 300 beds or more, 1 has added a new dimension of accuracy to both the red cell count and mean corpuscular volume (MCV). Indexes Red cel/ count-Before the 1960s, the graduai decline in reliance on indexes reflected the imprecision of the red cell count as measured in the hemocytometer counting chamber. The coefficient of variation was be•cou! ter Electronics, !ne. H ialeah. Florida.
282
tween 5.5% and 9.0% or even higher when the count was very low.2 Furthermore, chamber counts consistently overestimated cell numbers.3 With the advent of particle counters, not only were precision and accuracy sharply increased but the count was found to be lower than hitherto suspected. The coefficient of variation feil to between 1% and 2%. Mean corpuscular volume-Because of the imprecision of the red
One of a series of articles on orderlng and lnterpretlng laboratory tests whlch began ln April1978
cell count as measured in the hemocytometer chamber, the derived MCV (hematocrit [Hct]jred cell count [RBC]) was also imprecise. Furthermore, the normal range (87±5 cu J..L) was too low. With the advent of the particle counter, the lowered red cell count brought about an expansion of the upper end of the normal range of the MCV to 97 cu J..L. (Actually, 100 cu J..L is more commonly used as the cutoff point in clinicat practice.) In the Coulter S, the MCV is calculated directly. As each RBC passes through an electronic sensor, it generates an impulse and a change in electrical resistance proportional to its volume. The cumulative resistance divided by the number of impulses is translated into the MCV. Despite the fact that the Coulter S slightly overestimates the MCV, particularly in the low range,4 the data generated are considered adequate for clinicat purposes and an enormous improvement over the MCV calculated from the centrifuged hematocrit value and the hemocytometer red cell count (Hctf RBC). Hemog/obin-Hemoglobin levels as measured by standard and Coulter methods are identical and therefore warrant no further corn-
VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
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ment. Hematocrit-Even in normal blood, the hematocrit value measured by centrifugation slightly overestimates the true packed red cell volume because of plasma trapped between the cells. This minor overestimation (3%) is of little clinical significance when RBCs are normal in size and shape. However, plasma trapping may account for 20% or more of the packed red cell column (centrifuged hematocrit) in the presence of marked poikilocytosis, notably in sickle cell anemia. 5 To a lesser extent, this is also true of hypochromic states,s possibly on the basis of the associated poikilocytosis. The clinical implications are obvious. In the Coulter S, the hematocrit is not measured by centrifugation but rather calculated from the formula Hct = MCV x RBC. (This is merely a restatement of the basic calculation MCV = Hct/ RBC.) In determining the MCV, however, the Coulter S does not take poikilocytosis into account. It is sensitive to changes in volume only and is insensitive to changes in shape. Hence, the problem of plasma trapping no longer obtains. In normal individuals, the calculated hematocrit is 1.5% Jess than the centrifuged hematocriP In the presence of marked poikilocytosis, erroneous conclusions may be drawn if the physician switches from one method of measuring the hematocrit to the other in following the patient.
VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
Mean corpuscular hemoglobin (MCH)-Although sorne authors have recently espoused a low MCH as a sensitive measure of iron deficiency, 6 others have pointed out that since the MCH varies linearly with the MCV, it adds little in this situation. 7 With the improved accuracy of the red cell count, the MCH, like the MCV, has become respectable, although redundant. Mean corpuscular hemoglobin concentration (MCHC)- The MCHC was originally designed to reflect incipient hypochromasia, ie, decreased weight per unit volume (Hgb~/ Hct) in patients with evolving iron deficiency. In this function, it performed relatively weil. With the advent of electronic particle counters, however, the MCHC was found to be insensitive to ali but severe degrees of hypochromasia-for a curious reason. 8 In evolving iron deficiency, a degree of poikilocytosis is always present. Hence, because of the associated plasma trapping, the centrifuged hematocrit is spuriously high. Although the falling MCHC of evolving hypochromasia should primarily reflect a disproportionate fall in hemoglobin in relation to hematocrit, the effect is exaggerated by Patrick C. J. Ward Dr Ward is director of clinical laboratories. Mount Sinai Hospital, and associate professor of laboratory medicine and pathology, University of Minnesota Medical School. Minneapolis.
the simultaneously (but spuriously) increased hematocrit. The low MCHC of iron deficiency now equals Hgb~ 1Hctt rather than Hg~ 1Hct. Hence, an MCHC derived from a centrifuged hematocrit reflects both hypochromasia and poikilocytosis, the latter contributing significantly to the sensitivity of this measurement in detecting the mild hypochromasia of early iron deficiency. In the Coulter S method, the role of poikilocytosis in determination of the MCHC has been elimïnated, since the hematocrit is calculated rather than measured by centrifugation and therefore no plasma trapping is present. Hence, a factor (admittedly spurious) has been eliminated and the calculated MCHC is no longer as sensitive in detecting mild degrees of hypochromasia, such as might be anticipated in early iron deficiency. 8 The MCHC does fall in advanced iron deficiency, but the problem remains that hypochromasia may be visible on smears while the MCHC is normal. At the other end of the scale and by both methods, the MCHC may be effective in detecting sorne cases of congenital spherocytic anemia. When the MCHC is 36% or more and both hypertriglyceridemia and cold agglutinin disease have been excluded,9,IO the patient has congenital spherocytic anemia. The absence of such increases, however, does not exclude this disease. continued
283
LABORATORY MEDICINE CONTINUED
Downloaded by [Australian Catholic University] at 09:46 19 August 2017
With the advent of electronic particle counters, the precision and accuracy of the red cell count and MCV have increased considerably.
Diagnostic exercise The following brief test cases are based on the investigative process described in the preceding articles in this series on anemia. The final diagnosis is provided in each case. For reference, the normal ranges for red cell indexes suggested by Coulter Electronics, Inc, are given in table 1. Table 1. Nonnal values for red cell indexes• Index
Nonnal values
Males
Females
5.4±0.7 4.8±0.6 Red cell count (RBC) (x10"/cu mm) Hemoglobin (Hgb) (gm/dl)
16.0±2
14.0±2
Hematocrit (Hct)
47±5
42±5
87±7
90±9
Mean corpuscular hemoglobin (MCH) (pg)
29±2
29±2
Mean corpuscular hemoglobin concentration (MCHC)
34±2
34±2
Case 1 35-year-old black female with neckinjury. Routine admission Coulter S panel: RBC 4.77 Hgb 12.6 Hct 37.8 MCV 79 MCH 26.4 MCHC 33.1 Discussion The panel shows a very minor degree of microcytosis. There is no anemia. The discriminant function (DF') is positive. The smear is normal, ie, microcytosis of the degree present by MCV would be impossible to detect visually.
(%)
Mean corpuscular volume (MCV)
Case2 76-year-old white female with a long history of rheumatoid arthritis. Taking indomethacin and aspirin intermittently. Coulter S panel: RBC 3.96 Hgb 6.7 Hct 24 MCV 61 MCH 17.1 MCHC 27.4 Discussion The panel shows severe hypochromic microcytic anemia. The history atone is consistent with iron deficiency anemia (perhaps from drug-induced gastric bleeding), the anemia of chronic disease, or both. The DF' is positive. The MCV strongly suggests iron deficiency anemia, since the MCV of the anemia of chronic disease rarely falls below 72 cu J.l..u Nevertheless, an element of anemia of chronic disease cannot be ruled out.
(CU p.)
Investigation Serum iron (30 }.l.g/ dl), serum ironbinding capacity (474 p.gf dl).
(%)
*Coulter Counter Model S.
Conclusion Iron deficiency state without anemia. Further history of very heavy menses elicited.
Investigation Serum iron ( 15}.1.g/ dl), serum iron-binding capacity (178 J.l.g/dl), guaiac test (negative), upper gastrointestinal series (normal). Conclusion Not currently bleeding. Although the iron data are more consistent with anemia of chronic disease, there is quite probably an element of iron deficiency. Iron therapy started with a view to reversing the anemia to the extent that iron deficiency is causative. 11
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The hematocrit value determined by the centrifugation method slightly overestimates the packed red cell volume because of plasma trapping between ce lis. This error is compounded when poikilocytosis is present.
Case 3 72-year-old white female with long history of hematologie disorder. Hepatosplenomegaly. Coulter S panel:
Case4 31-year-old white male with four-year his tory of buming sensations and tingling in both feet. Coulter S panel:
RBC 6.26 Hgb 15.0 Hct 48.2 MCV 77 MCH 24.0 MCHC 31.4
RBC 4.14 Hgb 15.7 Hct 47.2 MCV 113 MCH 37.8 MCHC 32.8
Discussion The indexes show mild microcytosis, marginal hypochromasia, and erythrocytosis. The DF'isnegative. In the absence of hepatosplenomegaly, these data would ordinarily suggest thalassemia mi nor. The smear shows teardrop poikilocytosis. Hypochromasia not shown.
Discussion These data reveal macrocytosis without anemia. Patients presenting with macrocytosis but without anemia have been described as candidate occult alcoholics.u In the absence of vitamin 8 12 or folate deficiency, such macrocytosis may be the consequence of a direct effect of alcohol on the developing erythroblast 14 and precede anemia.
Investigation Serum iron (44 J.Lg/ dl), serum ironbinding capacity (380 J.Lg/ dl), hemoglobin electrophoresis (normal). Conclusions Polycythemia vera with mild iron deficiency. The indexes in polycythemia vera with iron deficiency anemia may simula te those of thalassemia minor. 12 The mild erythrocytosis and negative DF' are common to both disorders. The teardrop forms reflect splenomegaly and suggest a degree of evolving (secondary) myelofibrosis, ie, the "spent" phase of polycythemia vera.
VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
Case 5 50-year-old obese plethoric white male noted to have increased blood pressure on routine physical examination. Coulter S panel: RBC 6.62 Hgb 21.4 Hct 63.8 MCV 97 MCH 32.3 MCHC 33.4 Discussion These data reflect a polycythemic state. The smear shows a uniform cell.population. The MCV is at the upper limit of normal, a leve! usually encountered in the later decades of life. 15 In the presence of polycythemia, neither vitamin 8 12 nor folate deficiency merits serious consideration. It has been noted thatthe MCVtends to be increased by smoking, chronic hypoxia, and chronic carbon monoxide poisoning. 15 Any of these may be causally related to a polycythemic state.
Investigation Reticulocyte count (normal); serum vitamin 8 1", serum and red cell folates (normal); liver function tests (mildly abnormal). Conclusions The uniform macrocytosis in the smear in conjunction with the other test results favors liver disease. Long history of alcoholism finally elicited from the patient. Final diagnosis: alcoholic polyneuropathy.
Investigation Carboxyhemoglobin leve! (17% and 12% on two occasions). Conclusions History of smoking between 12 and 20 cigars a day elicited. Final diagnosis: smokers' polycythemia. 16 Hypertension felt to be unrelated.
continued
285
SLO.PHYLLIN-t GYROCAPS;J 60 mg., 125 mg., 250 mg. (theophylline, anhydrous) SLO.PHYLLIN® TABLETS 100 mg. and 200 mg. (theophylline, anhydrous)
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SLO.PHYLLINJr 80 SYRUP (theophylline, anhydrous) Composition: Slo-Phyllin"' Gyrocaps® (timed release capsules) contain Theophylline (anhydrous) in a special base !hat provides for a prolonged therapeutic affect. Each Slo-Phyllin-' 60 {white color, dye-free) Gyrocap~ contains 60 mg. of Theophylline (anhydrous). Each Slo-Phyllin-~ 125 (brown color) Gyrocap-~ contains 125 mg. of Theophylline (anhydrous). Each Slo-Phyllin' 250 (purple color) Gyrocap! contains 250 mg. of Theophylline (anhydrous). Slo-Phyllin"' tablets {white, scored, dye-free) contain prompt acting Theophylline in two strengths. Slo-Phyllm' 100 mg. tablet and Slo-Phyllin~ 200 mg. tablet. Slo-Phyllin·' 80 Syrup (orange color. nonalcoholic) contams 80 mg. of Theophylline (anhydrous) per 15 ml. (one tablespoonful). Indications: Slo-Phyllin •• is used in the trealment of asthma and other pulmonary disorders in which a reversible bronchoconstrictive element may be present such as chronic bronchitis and emphysema. Side EHects: Theophylline may cause gastric irritation, nausea, vomittng, and abdominal discomfort, headache, palpitation, !ali in blood pressure, central nervous system stimulation, and diuresis. Slo-Phyllin~ Gyrocaps .. are formulated in a timed release form to minimize these gastric complatnts. Precautions: Slo-Phyllin" should not be used concurrently with other formulas containing xanthine derivatives. Warnlng: Safety in human pregnancy has not been established Dosage and Administration: Slo-Phyllin"" Gyrocaps~ 60 mg.-125mg. -250mg. CHILDREN UNDER 12: The recommended dosage range is 3-5 mg./kg body weight every 8 hours. An initial dosage of 4 mg./kg. body weight every 8 hours to a maximum of 16 mg./kg./24 hours is recommended. If the dosage is to be increased, it should be done in small increments up to a maximum of 24 mg./kg./24 hours or 900 mg./24 hours whichever is less. If the patient is to be maintained at a near maximum of the recommended dosage levels, serum theophylline levels should be determined. ln children, not more than 8 mg./kg. every 8 hours should ordinarily be given. If side affects should occur, the dosage should be reduced by 1 mg./kg./dose. ADULTS AND CHILDREN OVER 12: An initial dosage of 4 mg./kg. body weight every 8 hours is recommended. The recommended median dose is 8 mg./kg. every 8 hours. This dosage can be approached by increasing the initial dose by increments of 60 mg. to 125 mg. at 3 to 4 day intervals as long as adverse affects are not achieved. Because of the risk of reaching taxie serum theophylline levels (above 20 ,..g.lml.), serum theophylline concentrations should be obtained il higher doses are to be maintained.
The average adult dose is 930 mg./24 hours. However, sorne individuals may require doses as htgh as 2000 mg./24 hours. For greater flexibility and easier titration of dosage. Slo-Phyllin~· Gyrocaps·"' are available in 3 dosages-60 mg, 125 mg., and 250 mg. These dosages may be used interchangeably or complementary to one another in arder to achieve the desired dosage level. Slo-Phyllin-' Tablets and Slo-Phyllin~ 80 Sy!.l.!f,l Theophyllinize (titrate) each patient using Slo-Phyllin® at the recommended dosage of 3-5 mg./kg. body weight every six hours. lnitially the lower dosage should be administered, then the dosage may be increased if optimal bronchodilator affects are not achieved. lt is generally advised thal a dosage of 5 mg./kg. body weight every six hours not be exceeded unless it is possible to monitor serum theophylline concentrations during therapy si nee it has been establtshed that signtficant variations occur among individuals in the rate at which the drug is eliminated from the body Recommended Dosage of SLO.PHYLLIN"' Tablets tor Various Body Welghts
1 Weight lbs.
Dose (in mg)
1
3 mg/kg 4 mg/kg 5 mg/kg 6 mg/kg
kg
22 10 33 15 44 20 55 25 66 30 88 40 110 50 132 60 154 70 176 80 198 90 220 100
30 45 60 75 90 120 150 180 210 240 270 300
40 60 80 100 120 160 200 240 280 320 360 400
50 75 100 125 150 200 250 300 350 400 450 500
60 90 120 150 180 240 300 360 420 480 540 600
Administered every six hours. Recommended Dosage of SLO.PHYLLIN"' 80 Syrup for Varlous Body Weights
f Weight
Dose (in tsp.)
lbs.
kg
3 mg/kg
20 40 60 79
9 18 27 36
1 tsp. 2 tsp. .3 tsp. 4 tsp.
5 mg/kg
1 VJ tsp.
1V2 tsp. 3 tsp. 5 tsp. 6V2 tsp.
4 tsp . 5 tsp.
CONTINUED
Case6 42-year-old white female undergoing preemployment physical examination in hospital. Coulter S panel: RBC 3.92
Hgb 13.5 Hct 36.8 MCV 94 MCH 34.4 MCHC 36.5 Discussion Aside from the slightly low red cell count (which is difficult to explain except perhaps on the basis of lysis of sorne ce lis during the Coulter S dilution process), the single finding demanding attention is the increased MCHC. The patient is not anemie, ie, hemoglobin is 13.5 gmfdl.
1
4 mg/kg
2v2 tsp.
LABOAATOAY MEDICINE
Administered every six hours. The therapeutic serum theophylline concentration is considered to be between 10 and 20 ,..g.tml. This range may best be reached by individualizing the patient's dosage while concomitantly monitoring the serum theophylline concentrations. Slo-PhyllinJr 80 Syrup U.S. Patent #3928609 How Supplied: Slo-Phyllin® Gyrocaps"'-Bottles of 100 and 1000 unit dose pkgs. (125 mg. and 250 mg. only) Syrup-Pints and gallons unit dose botties, 5 ml. and 15 ml. Tablets-Bottles of 100 and 1000 unit dose pkgs.
Innstigation Osmotic fragility (increased). Conclusion Even without the smear, these data are collectively diagnostic of congenital spherocytosis. (Actually, the increased MC H C per se is virtually diagnostic of this disease; the increased osmotic fragility merely supports the diagnosis.)
-DDDNER 1!!1
LABDRATDRIEB, INC.
Subsidiary of: William H. Rorer, lnc. Fort Washington, PA 19034 VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
For detecting hypochromasia, the MCHC determined by electronic partie le counters is less sensitive than that determined by older methods.
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Case 7 60-year-old female with myxedema and diabetes. Coulter S panel: RBC 3.89 Hgb 17.4 Hct 34.6 MCV 88 MCH 42.1 MCHC 47.3 Discussion These data are unacceptable, since the normal ratio of roughly 3: 1 between hematocrit and hemoglobin does not obtain. One or the other test result is spurious. In this context, therefore, the high MCHC (Hgb/ Hct) is invalid (although arithmetically correct). The diagnostic possibilities are therefore hypertriglyceridemia and cold agglutinin disease rather than congenital spherocytic anemia.
hemoglobin determination by causing turbidity in the red celllysate. The derived indexes (MCH and MCHC) are therefore also rendered spurious. The correct indexes may be obtained by resuspending the RBCs in physiologie saline solution. 9 More simply, a reasonable approximation ofthe true hemoglobin value may be derived by dividing the hematocrit by 3. (lt should be understood that the hematocrit value is valid, since it derives from two measurements unaffected by hyperlipidemia, ie, red cell count and MCV.) Next month: A practical approach to diagnosis of infectious mononucleosis. Series coordinator: M. Desmond Burke, MD, associate pathologist, Mount Sinai Hospital, and associate professor of laboratory medicine and pathology, University of Minnesota Medical School, Minneapolis. Address reprint requests to Patrick C. J. Ward. MD. Mount Sinai Hospital, 2215 Park Ave, Minneapolis, MN 55404.
Investigation Cold agglutinin test (negative; further, RBCs normal in smears, with no evidence of autoagglutination in smears prepared at room temperature). Blood lipid studies: cholesterol (600 mg/ dl), triglycerides (12,600 mg/dl). Serum markedly hyperlipemic. Conclusion Hyperlipidemia superimposed on very mild normochromic normocytic anemia. Recent data suggest that hyperchylomicronemia rather than hypertriglyceridemia is responsible for aberrent indexes of this type. 9 Chylomicrons interfere with
VOL 65/NO 5/MAY 1979/POSTGRADUATE MEDICINE
References l. Cunningham LO, Rising JA: Erythrocytic microcytosis: Clinical implications in 100 patients. Am J Med Sei 273:149-155, 1977 2. Hattersley PG: Macrocytosis of the erythrocytes: A preliminary report. JAMA 189: 997-999, 1964 3. HamiHon PJ, Davidson RL: The interrelationships and stability of Coulter S-determined blood indices. J Clin Pathol 26:700705, 1973 4. England JM, Down MC: Measurement of the mean cell volume using electronic particle counters. Br J Haematol 32:403409, 1976 5. England JM et al: Re-assessment of the reliability of the hematocrit. Br J Haematol 23:247-256, 1972 6. Griner PF, Oranburg PR: Predictive values of erythrocyte indices for tests of iron, folie acid and vitamin B, deficiency. Am J Clin Pathol 70:748-752, 1978 7. Croft RF et al: Red cell indices in megaloblastosis and iron deficiency. Pathology 6:107-117, 1974 8. Rose MS: Epitaph for the MCHC. Br Med J 2:169, 1971 9. Gagne C et al: Effect of hyperchylomicronemia on the mea~urement of hemoglobin. Am J Clin Pathol68:584-586, 1977 10. Hattersley PG et al: Erroneous values on the Mode! S Coulter Counter due to high liter cold agglutinins. Am J Clin Pathol 55:442446, 1971 11. Cartwright GE, Lee GR: The anemia of chron!c disorders. Br J Haematol21:147-152, 1971 12. Hamblin TJ: Differentiation of iron deficiency from thalassemia trait by routine blood-count. (Letter) Lance! 1:676, 1973 13. Unger KW, Johnson D Jr: Red blood cell mean corpuscular volume: A potential indicator of alcohol usage in a working population. Am J Med Sei 267:2tll-2tl9, 1974 14. Wu A et al: Macrocytosis of chronic alcoholism. Lance! 1:tl29-831, 1974 15. Okuno T: Red cell size as measured by the Coulter Mode! S. J Clin Pathol 25:599.{)02, 1972 16. Smith JR, Landaw SA: Smokers' polycythemia. N Engl J Med 298:6-10, 1978
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