Monitoring of oral anticoagulation by an amidolytic factor X assay. A long-term study in 42 patients.

The validity of the amidolytic Factor X assay for the control of long term oral anticoagulation (OA) was investigated in 42 patients randomized into 2 groups; PT group (anticoagulant dosage according to PT) and F.X group (anticoagulant dosage based on F.X). An independent expert's dosage according to F.X served for analysis in the former group. In the F.X group the F.X based dosage was considered valid only when not differing by more than 15% from the expert's PT based dosage. Confirming the good correlation between PT and F.X the study further demonstrates that the changes from one control to the next one, delta PT and delta F.X, too, are significantly correlated (r = 0.58, p less than 0.001, n = 217). In over one third of the periods the dosage proposals based on PT and F.X were identical and differed by more than 15% in only 12/217 instances. Our results justify a large trial on the control of OA by the amidolytic F.X assay.