An Evaluation of Currently Available Methods for Plasma Fibrinogen
An assessment of fibrinogen concentration is basic to any investigation of clotting dysfunction and often an estimate of fibrinogen level is needed rapidly as an indication of consumptive coagulopathy or fibrinolysis. Fibrinogen levels in a variety of clinical plasma samples were assessed concurrently by several methods. Results were correlated against a reference method based on Ancrod-clottable fibrinogen and calibrated by U.V. absorbance with alkaline solutions of carefully dried fibrin standard. The best correlations with the reference method were achieved by an immunologic method using the Centrifichem principle and by heat precipitation with quantitation by packing in micro-haematocrit tubes. A modified clot opacity method also gave acceptable results. The turbidimetric ammonium sulphate and sodium sulphite precipitation methods correlated less well with the reference method, and in particular the sodium sulphite technique gave high apparent fibrinogen levels with jaundiced plasmas. Neither of the turbidimeteric methods were useful for fibrinogen levels below 50mg/dl. The thrombin time method showed excellent sensitivity to fibrinogen, even at very low fibrinogen levels, but did not correlate well with the reference method. This apparently conflicts with the findings of a recent CAP survey which strongly favoured the thrombin time method. We believe there is a danger that such surveys promote test methods on which there is good inter-labotatory agreement, but which may not be specific in function.