Comparability of serum and plasma concentrations of haemostasis activationmarkers

Since serum and plasma D-dimer concentrations correlate very well, we evalu ated the comparability of other haemostasis activation markers in plasma an d serum. Prothrombin fragment F1+2, fibrin monomer and D-dimer concentratio ns were measured with commercially available immunoassays in serum and plas ma. Serum to plasma ratios were evaluated to determine the direct (prothrom bin fragment F1+2) and indirect (fibrin monomer, D-dimer) downstream influe nce of prothrombinase on the serum to plasma comparability. Prothrombin fra gment F1+2 serum and plasma concentrations did not correlate (R-2 = 0.09, n s), while an unexpected high degree of correlation was found for fibrin mon omer (R-2 = 0.66, p < 0.001), and, as expected, a very good correlation was found for D-dimer (R-2 = 0.94, p < 0.001). Median serum to plasma ratios d ecreased from prothrombin fragment F1+2 (16.26) to fibrin monomer (2.24, p < 0.001) and D-dimer (1.00, p < 0.001), following a highly linear relations hip (R-2 = 0.93). Plasma and serum concentrations of the evaluated markers correlate the better the farther from prothrombinase activity the respectiv e marker is generated. Serum is not suitable for prothrombin fragment F1+2 measurements, whereas fibrin monomer serum concentrations seem of value for research applications. With the used assay, serum seems an appropriate mat rix for clinical D-dimer measurements. This would considerably simplify tes ting strategies. Validation in further clinical trials is needed.