The aim of our work was to test the new direct method for the determination of total plasma homocysteine adapted to clinical chemistry analyser Synchron LX 20, Beckman Coulter. The results obtained with HCY-Homocysteine Reagent Kit (part No. CC202), Carolina Liquid Chemistries, California were compared with the immunoassay Abbott Axsym results. Analytical method: The kit utilizes a reaction of homocysteine and L-serine to form cystathionine catalyzed by cystathionine β-synthase followed by the cystathionine – β-lyase catalyzed conversation of cystathionine to homocysteine, pyruvate and ammonia. The rate of pyruvate production can be measured by inclusion of LD and NADH in the reaction mixture and is directly proportional to the concentration of homocysteine. Assay conditions on the analyser Synchron LX 20, Beckman Coulter: reaction type – rate 1, primary wavelenght 340 nm, secondary wavelenght 380 nm, three reaction components, final assay mixture contain: Lactate Dehydrogenase (LD) > 65 KU/L, serine = 13 mmol/L, NADH = 1.06 mmol/L, Cystathionine -β-Synthase > 28 KU/L, Cystathionine -β-Lyase > 8 KU/L.The ratio of sample: reagent is 1:10. The method was calibrated with two calibrators (0.0 and 26.5 µmol/l) from the kit. For quality control we used controls by firm Abbott, Homocysteine controls L,M,H (lot. 90012HP00, exp. 2003-09-19). The levels of controls were: 7.0, 12.5 and 25 µmol/l. Precision within run was performed in level of Hcy concentration 4.5; 9.5; 14.8 and 15.5 µmol/l. There were measured 7 plasma samples in each level of concentration. CV – 10.76%, 1.79%, 3.34% and 1.21% resp. Precision between runs was established on three levels of Hcy concentration (7; 12.5 and 25 µmol/l) over 5 days. During this period we did not recalibrate the method. CV = 3.33%, 2.89%, 3.15% resp. bias 108%, 102%, 96.5% resp. linearity of the method was tested by recovery study. The sample with homocysteine concentration 82 µmol/L was diluted and recovery was calculated for concentrations 82; 41;20.5; and 5.1 µmol/l, respectively. The recovery: 106%, 105%, 108%, 99% and 102% was established. Further we compared homocysteine values measured on the same samples on analyser Synchron LX 20 and AxSym Abbott.A total of 34 samples were measured with level of Hcy from 1.2 to 52.6 µmol/l.Pearson’s correlation coeficient was r = 0.9976,P<0.0001. Regression equation:Y = 0.9793 X + 0.0049;Y = Hcy (AxSym), X = Hcy (Synchron LX 20). Intercept was not statistically different from zero, P<0.9816, slope was not statistically different from one, P = 0.0975. Any relation between values of differences and average value was deterrmined (Blad-Altman). Conclusion: Homogeneous enzymatic method for determination of plasma total homocysteine (HCY – Carolina, Liquid Chemistry Corp.) applied to clinical chemistry analyser Synchron LX 20, Beckman Coulter is a quick, simple, efficient and economical method according to our experience.

        Key words: tHcy, homogenous enzymatic method, determination of tHcy.