Thrombin treated plasma employed as a standard for determination of soluble fibrin

The Coa-set Fibrin Monomer test (CFM-test) is a quantitative method for determination of soluble fibrin in plasma. The fibrin standard of the CFM-test is produced by bathroxobin conversion of purified fibrinogen to fibrin. Plasma treated with minute amounts of thrombin may be considered as a more physiological way of preparing fibrin monomers. Therefore, we have employed such thrombin treated plasma (TTP) as an alternative fibrin standard for the CFM-test. The fibrin concentration of the TTP was determined indirectly by quantitation of released fibrinopeptide A. The TTP was stable during freezing, thawing and storage for 3 months at -70 degrees C. The standard curve obtained using TTP as a standard was linear in the range of 0-275 nmol/l fibrin in plasma, but the slope of the line was less steep than the original standard curve. This difference was probably due to the greater plasminogen activating effect of bathroxobin digested fibrinogen compared to soluble fibrin generated in plasma by thrombin, as observed in a previous study. Because of the less steep slope of the alternative standard curve, fibrin levels in plasma samples from 20 healthy volunteers and 25 patients were found to be higher employing TTP as a standard. Preparation of a fibrin standard by incubation of plasma with minute amounts of thrombin will to some extent mimic the process of fibrin generation in vivo. Since we have found a satisfactory stability of such a standard during freezing, thawing and storage, we think the TTP standard might be useful for quantitation of soluble fibrin in plasma.