663

Letters to the editor

jointly than individually. There can be a physiological basis for this. If the raised level of myocardial enzymes is the direct consequence of myocardial necrosis (Sobel et al, 1972) and the raised level of FDP indicates a fibrinolytic response to a previous thromboembolic episode (Merskey and Johnson, 1971) then the patient should be suffering from an extensive myocardial lesion and its consequential thromboembolic complications. Interestingly, none of our three patients who had a raised FDP level with low enzyme levels died. Therefore perhaps the opinion that a high FDP level is a sign of a poor prognosis in acute myocardial infarction should be revised unless it is also associated with raised myocardial enzymes. J. AZNAR, C. TORMO, J. L. GARCIA RAMOS, M. J. COLOMER, V. VILA, and M. RUANO

Department of Clinical Pathology, Intensive Care Unit, Ciudad Sanitaria 'La Fe',

Valencia, Spain. References

Almer, L. O., Hedner, U., and Nilsson, I. M. (1972a). Fibrin degradation products in the early differential diagnosis of acute myocardial infarction. Thrombos. Res., 1, 59-69. Almer, L. O., Hedner, U., and Nilsson, I. M. (1972b). Serum fibrin/fibrinogen degradation products in acute myocardial infarction. (Letter.) Lancet, 1, 689-690. Baele, G., Mussche, M., and Vermiere, P. (1972). Serum fibrin/fibrinogen products in acute myocardial infarction. (Letter.) Lancet, 1, 689-690. Baele, G., Mussche, M., Vermiere, P., and Pannier, R. (1973). Determination des produits de degradation du fibrinogene et de la fibrine (P.D.F.) A la phase aigue de l'infarctus. Arch. Mal. Coeur, 66, 427-429. Choudhury, S. Lal, Edge, J. R., and Stansfield, D. (1975). Serum fibrin/fibrinogen degradation products as a prognostic index in acute myocardial infarction. J. clin. Path., 28, 821-824. Konttinen, A. and Somer, H. (1973). Specificity of serum creatine kinase isoenzymes in diagnosis of acute myocardial infarction. Brit. med. J., 1, 386-389. Merskey, C. and Johnson, A. J. (1971). The clinical significance of fibrinogen-fibrinrelated antigen in serum. Scand. J. Haemat., Supplement, 13, 313-315. Merskey, C., Lalezari, P., and Johnson, A. J. (1969). A rapid, simple, sensitive method for measuring fibrinolytic split products in

human serum. Proc. Soc. exp. Biol. (N. Y.), 131, 871-875. Morris, K. G., Hayes, M. J., and Hampton, J. R. (1974). Fibrin degradation products and the "251-labelled fibrinogen test in patients with myocardial infarction. Europ. J. Cardiol., 2, 35-38. Okuno, T. and Nelson, C. (1974). Value of determination of serum fibrin-fibrinogen degradation products in acute myocardial infarction. Amer. J. clin. Path., 61, 155-159. Peel, A. A. F., Semple, T., Wang, I., Lancaster, W. M., and Dall, J. L. G. (1962). A coronary prognostic index from grading the severity of infarction. Brit. Heart J., 24, 754-760. Sobel, B. E., Bresnahan, C. F., Shell, W. E., and Yoder, R. D. (1972). Estimation of infarct size in man and its relation to prognosis. Circulation, 46, 640-648. Wagner, G. S., Roe, G. R., Limbird, L. E., Rosati, R. A., and Wallace, A. G. (1973). The importance of identification of the myocardial-specific isoenzyme of creatine phosphokinase (MB form) in the diagnosis of acute myocardial infarction. Circulation, 47, 263-269.

specificity and sensitivity. Contrary to these authors we have found that, apart from being extremely rapid, this method is more sensitive and less susceptible to interference by other commonly abused drugs than is the method of Routh (1968), but the presence of high concentrations of phenylbutazone may give misleading results (table). The method used in our laboratory is as follows: To 1 ml serum or plasma add 1 g NaCI (approx) and 10 ml diethyl ether (Analar). Mix gently for 30 seconds by inversion, and as it is very rare for emulsions to form the ether may be decanted directly into a quartz cuvette and the absorbance read at 250 nm against an ether blank. A serum-based standard should also be taken through the procedure. The assay is linear to 1000 pmol/l. Precision of the method was excellent (CV = 1-8% at 750 ,umol/l, N = 16). One possible objection to the method is that falsely high results might be obtained due to evaporation of the ether. This has been Rapid estimation of paracetamol in negligible in our experience, the absorbance of paracetamol in ether increasing by plasma less than 0 5 % per minute at 25°C and by Many methods for the determinaton of 1 % per minute at 37°C. paracetamol in serum and plasma have R. J. SPOONER, P. C. REAVEY, AND been described in recent years, and of L. MCINTOSH these the method of Routh et al (1968) has Department of Clinical Biochemistry, gained widespread acceptance. The Royal Infirmary, method uses the differential absorbance Glasgow G4 OSF at 266 nm of an acidified and alkalinized extract in order to minimize interference by salicylate. This choice of References analytical approach means that the method is relatively insensitive (.- 100 Dordoni, B., Willson, R. A., Thompson, ,umol/l) and that both barbiturates and R. P. H., and Williams, R. (1973). Reduction of absorption of paracetamol by phenylbutazone interfere. (We enactivated charcoal andcholestryramine:A countered five cases of mixed overdose possible therapeutic measure. Brit. med. involving paracetamol and barbiturate in J., 3, 86-87. 1975.) Routh, J. I., Shane, N. A., Arredondo, E. G., Dordoni et al (1973) described a rapid and Paul, W. D. (1968). Determination of method for the determination of paraN-acetyl-p-aminophenol in plasma. Clin cetamol to which they ascribed a lack of Chem., 14, 882-889. Drug

Concentration

Phenobarbitone

400 gmol/I 10 mmol/l 400 Amol/I 300 jAmol/I 450 jAmol/1 850 Amol/1

Interference

(as Salicylate Methaqualone Penylbutazone Glutethimide Carbromal

pmol/l paracetamol)

25 25 50 200 0 0

Table Effect of the presence of other drugs on the determination of paracetamol

Letter: rapid estimation of paracetamol in plasma.

663 Letters to the editor jointly than individually. There can be a physiological basis for this. If the raised level of myocardial enzymes is the d...
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