Evaluation of a new chromogenic substrate assay for the measurement of the prothrombin time.

The chromogenic prothrombin time assay Nycotest Chrom was evaluated and compared with another chromogenic assay (Chromoquick) and with the well-known coagulometric Thrombotest. The intra-assay variation of the test was satisfying both in the normal range (CV = 3.6%) and in the therapeutical range of oral anticoagulation (CV = 3.5%). These values were somewhat higher than those of the Chromoquick test (1.3% and 1.1%) and those of the Thrombotest (2.3% and 2.5%). The inter-assay variation coefficient amounted to 3.3% in the normal range and in the therapeutical oral anticoagulation range to 4.4%. The respective values for the Chromoquick test were somewhat lower (2.2% and 3.9%), those of the Thrombotest in the normal range were also lower (2.1%), and in the therapeutical range they were much higher (9.2%). The coefficients of correlation of the Nycotest Chrom test in the therapeutical range were highest when comparing them with those for the Chromoquick test (r = 0.97; p < 0.0001) and somewhat lower in comparison with the Thrombotest (r = 0.95; p < 0.0001). The results of the three methods paralleled also in the starting phase of oral anticoagulation treatment. Storage at 4 degrees C and at 25 degrees C showed good stability of the Nycotest Chrom reagent for up to 24h. We conclude that the Nycotest Chrom assay is well suited for the measurement with a centrifugal fast analyser, which is attractive on behalf of the usually large series of request for prothrombin time measurements when monitoring oral anticoagulation therapy.(ABSTRACT TRUNCATED AT 250 WORDS)