A new test for measuring soluble fibrin in plasma with a high predictive value for thrombotic disorders

Fibrin formation is initiated by thrombin which releases the fibrinopeptides A and B from fibrinogen. In vivo, fibrin molecules form soluble complexes with fibrinogen. At a certain threshold concentration, fibrin-fibrin interactions prevail and insoluble aggregates are formed on site. Soluble fibrin is considered to be an early biochemical marker for intravascular fibrin formation and impending thrombotic events such as deep venous thrombosis (DVT), disseminated intravascular coagulopathy (DIC) and pulmonary embolism (PE). A new test was developed on the basis of a monoclonocal antibody directed against an alternative fibrin specific neo-epitope located on the gamma-chain of fibrinogen; γ-(312-324). In addition, it was possible to prepare a stable and lyophilized thrombin-generated Soluble Fibrin reference material. Assay conditions, e.g. coat-Ig concentration and buffer, and sample and conjugate dilution and incubation times and temperature were optimised. The present assays was found to be specific (no interference of homologous antigens, e.g. fibrin(ogen) degradation products), accurate (intra-assay variation; 5.2-6.5%) and reproducible (inter-assay variation; 4.3-9.6%), and is thus highly suited to measure soluble fibrin levels in a plasma milieu. The mean normal for soluble fibrin, as determined in samples obtained from apparently healthy volunteers, was 42 ng/ml (95% Cl 38-45 ng/ml, N=81 ). Soluble fibrin levels were found to be significantly increased, by Mann-Whitney LiTest, in patients with confirmed diagnosis of: DVT; mean=358 ng/ml, 95% CL 162-553, n=36, p < 0.0001 vs normal, DIG; mean=109 Ing/ml, 95% Cl 720-1461 ng/ml, n=21,p<0.0001 vs normal, and PE; mean=588 ng/ml, 95% CL442-735 ng/ml, n=29, p<0.0001 vs normal. Using the 97% limit of the normal reference range as cut-off point, i.e. 77 ng/ml, the overall positive predictive value of the present test for thrombotic disorders is 97% (negative predictive value 93%, sensitivity 98%, specificity 97%).