An evaluation of currently available methods for plasma fibrinogen.

Fibrinogen levels in a variety of clinical plasma samples were assessed concurrently by several methods. Technics that appeared to provide the best improvements over the basic varieties of methods for fibrinogen assay were used. Results were correlated against a reference method based on Ancrod clottable fibrinogen and calibrated by ultraviolet 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 microhematocrit tubes. A modified clot opacity method also gave acceptable results. The turbidimetric ammonium sulfate and sodium sulfite precipitation methods correlated less well with the reference method, and in particular, the sodium sulfite technic gave high apparent fibrinogen levels with jaundiced plasmas. Neither of the turbidimetric methods were useful for fibrinogen levels below 50 mg/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.