An evaluation of chromogenic substrates in the control of oral anticoagulant therapy.

A comparison has been made between the prothrombin time test using British Comparative Thromboplastin (BCT) and four modified amidolytic assays in the assessment of laboratory control of oral anticoagulant administration in short-term and long-term patients. The results were also correlated with the APTT and specific assays for factors VII and X based on established coagulation techniques. The chromogenic substrate assays did not give as close agreement with the BCT as the clotting assays for factors VII and X. A combination of the amidolytic factor II and X results did not improve the correlation. Agreement with the BCT was better in long-term patients with the substrates but there was no obvious advantage between the factor II and X amidolytic methods in this group. The development of a specific amidolytic assay for factor VII should be considered based on the evidence of this study although its reliability for oral anticoagulant control would need to be validated by clinical trial. In the interim, it may be anticipated that thromboplastins showing less sensitivity than BCT to factor VII would give a better correlation with the amidolytic assays.