EVALUATION OF AN AUTOMATED PHOTOMETRIC FIBRINOGEN ASSAY

A recently-introduced automated method for the determination of plasma fibrinogen is based on the principle of von Clauss, combined with pho tometric detection: after addition of thrombin, the coagulation time i s determined by measuring the change in absorption at 405 nm. This met hod was evaluated and compared with the original coagulometric Clauss assay and with the prothrombin time (PT)-derived automated method. The inter-assay coefficient of variation of the Clauss-derived assay was lower (14.1, 3.8 and 4.6%) than the PT-derived assay (16.1, 7.5 and 10 .5%, respectively) at all three fibrinogen levels tested (1.2, 4.0 and 7.5 g/l). The correlation between the assays was investigated accordi ng to the method of Passing and Bablok and could be described as follo ws: Clauss-derived = 0.79 (PT-derived) + 0.66; Clauss-derived = 1.12 ( Clauss) + 0.143. The interference of heparin (< 1.5 U/ml), haemoglobin (< 30 mu mol/l), bilirubin (< 200 mu mol/l) and triglycerides (< 5.5 mmol/l) in the Clauss-derived assay was negligible. The effects of fib rinogen degradation products on the Clauss-derived assay were comparab le with the effects on the Clauss assay, in contrast to the effects on the PT-derived assay. In conclusion, the Clauss-derived assay is a sp ecific and precise automated method to determine fibrinogen concentrat ions in plasma, which is not liable to interference from different pat hophysiological substances.