INACCURACY OF THE DERIVED FIBRINOGEN MEASUREMENT

The 'derived' fibrinogen method is commonly used for the measurement o f plasma fibrinogen. This method is not a direct quantitation of plasm a fibrinogen, but an estimation of the fibrinogen concentration from t he clotting curve of the prothrombin time on automated photo-optical c oagulometers. An increasing number of laboratories are now routinely u sing this method to cope with increasing demands for fibrinogen testin g. To study the suitability of this method for routine laboratory use a total of 58 samples, 20 healthy normals and 38 from other patient gr oups were tested by the 'derived' and Clauss fibrinogen methods on the ACL 300R. The results clearly demonstrated that 'derived' fibrinogen assay values were significantly higher than the Clauss measurements. T he discrepancy between 'derived' and Clauss fibrinogen levels was grea ter in certain patient groups, e.g. patients receiving oral anticoagul ants, than in normal controls. Some patients with documented hypodysfi brinogenaemia with low fibrinogen levels by Clauss assay gave normal ' derived' fibrinogen values. Although the 'derived' fibrinogen assay is rapid, economical and easily available to laboratories with suitable instruments, this study shows that it lacks standardization and is ina ccurate compared with the Clauss assay.