Multicenter evaluation of a new chromogenic factor X assay in plasma of patients on oral anticoagulants

A new factor X (FX) assay based on the chromogenic substrate S-2337 was compared with the coagulation screening method Thrombotest (TT) in 1431 plasma samples from 188 patients followed up for 6–8 months on long-term oral anticoagulants. In all the participating laboratories, the results of the methods were highly correlated (P < 0. 001). The FX values corresponding on the regression line to a TT therapeutic interval of 5–15 per cent ranged from 8 to 36 per cent in different laboratories. The results of the two methods were highly concordant in classifying the patients within or outside the therapeutic interval. The precision of the FX method was no better than that of TT both in normal and pathological samples. On the basis of these findings, the FX chromogenic method appears to be a potentially promising new approach to the problem of anticoagulant therapy control, providing that a longitudinal study confirm its clinical suitability.