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 photometric detection: after addition of thrombin, the coagulation time is determined by measuring the change in absorption at 405 nm. This method 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 according to the method of Passing and Bablok and could be described as follows: 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 micromol/l), bilirubin (< 200 micromol/l) and triglycerides (< 5.5 mmol/l) in the Clauss-derived assay was negligible. The effects of fibrinogen degradation products on the Clauss-derived assay were comparable 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 specific and precise automated method to determine fibrinogen concentrations in plasma, which is not liable to interference from different pathophysiological substances.