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

Abstract

van Wersch J. W. J. Evaluation of a new chromogenic substrate assay for the measurement of the prothrombin time. Scand J Clin Lab Invest 1993; 53: 563-568.

The chromogenic prothrombin time assay Nycotest Chrom^R was evaluated and compared with another chromogenic assay (Chromoquick^R) and with the well-known coagulometric Thrombotest^R. 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^R test (1.3% and 1.1%) and those of the Thrombotest^R (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^R test were somewhat lower (2.2% and 3.9%), those of the Thrombotest^R 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^R test in the therapeutical range were highest when comparing them with those for the Chromoquick^R test (r = 0.97; p < 0.0001) and somewhat lower in comparison with the Thrombotest^R (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°C and at 25°C showed good stability of the Nycotest Chrom^R reagent for up to 24 h.

We conclude that the Nycotest Chrom^R assay is well suited for the measurement with a centrifugal fast analyser, which is attractive on behalf of the usually large series of requests for prothrombin time measurements when monitoring oral anticoagulation therapy. It showed a good performance and with other tests a comparable performance, but the simultaneous use of the studied tests cannot be recommended.

Key Words:

• chromogenic substrate
• prothrombin time