The effect of increased contact activation time on the activated partial thromboplastin time.

With the kaolin-cephalin activated partial thromboplastin time technic, the plasmas of persons who have Fletcher factor deficiency have shown considerable shortening of clotting times when contact activation has been lengthened from 3 (PTT-3) to 10 minutes (PTT-10). The authors demonstrate that in plasma of most normal individuals, and in coagulopathies of other sorts, only slight shortening usually occurs. Abnormal shortening occurs in plasmas of a few otherwise normal people, the "slow activators," and patients receiving coumarin drugs, who have greatly prolonged prothrombin times.