Prothrombin Activity of Blood of the Newborn.

Abstract

When the plasmas of a newborn infant and of a normal adult are mixed in varying proportions, the prothrombin time which is 12 seconds for each remains unaltered. This suggests that the active prothrombin which is the determinant of the prothrombin time is the same in both plasmas. Newborn blood lacks prothrombinogen which accounts for the low prothrombin as measured by the 2-stage prothrombin test, since the latter procedure measures total prothrombin but fails to differentiate between active prothrombin and prothrombinogen.