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Dr. Pál László, 2nd Department of Medicine, University Medical School, POBox 12, H-4012 Debrecen (Hungary) bin time test and this might raise some new requirements against the thromboplastin. The reagent dependency of the derived fibrinogen method was investigated on ELECTRA 900C (Medical Laboratory Automation, Pleasantville, N.Y.). This coagu-lometer printed out not only the fibrinogen value of the sample, but the delta optical density (DOD) value, too. Simplastin Excel and Simplastin Excel S, two rabbit brain thromboplastins of Organon Teknika (Durham, N.C.) along with Innovin, a dried, recombi-nant human reagent from Baxter Recently, a new method of serial fibrinogen determination was developed using a well-known procedure applied to widely available photo-optical coagulometers [1]. The derived fibrinogen method is based on the determination of the differences in optical density caused by the conversion of fibrinogen to fibrin. This method offers some advantages: it measures only clotable fibrinogen, it is not sensitive to fibrinogen/fibrin degradation products, and proved to be highly reproducible as well [2, 3]. The derived fibrinogen method is performed together with prothromTable 1. Correlation of DOD: Innovin and Simplastin Excel versus Simplastin Excel S (n = 80) Innovin Simplastin Excel Slope Intercept r Sχ/γ 1.387(0.0385) 0.0043 (0.0078) 0.9713 0.0242 2.263 (0.0604) -0.0202(0.0122) 0.9733 0.0380 Values in parentheses represent standard error. In all cases the p values were < 0.0001. r = Regression coefficient; Sχ/γ = standard error of y estimate. Healthcare (Miami, Fla.), were investigated. The international sensitivity index values for photooptical coagulometers were 1.96, 1.13 and 0.98, respectively. According to the laboratory standard procedures, blood samples of 20 healthy persons and 60 unselected patients were collected and stored at -40¤C until assay. All plasma samples were obtained in accordance with the Medical Ethical Committee regulations of our institute. For each reagent a reproducibility study was performed using a normal and two abnormal control plasmas for monitoring coagulation. The intra-assay variation of prothrombin time with the thromboplastins did not exceed 2%. The quality control was assessed each working day, the inter-assay variation was less than 3%. The investigation of DOD correlation with different reagents, Innovin and Simplastin Excel versus Simplastin Excel S, gave linear regression lines (table 1). The intercepts were very close