Concentration of Prothrombin in Blood of Babies (3 to 7 Days Old)

Abstract

The ease with which nutritional deficiency states develop in young infants suggests the advisability of studying their prothrombin level, since it is now known that vitamin K is required for the synthesis of this clotting factor.

Blood was obtained by venipuncture from normal healthy infants varying in age from 3 to 7 days. The prothrombin was quantitatively determined by the senior author's method 1 on both the undiluted plasma and on plasma diluted with an equal volume of saline solution. Typical cases of this series are presented in Table I.

The results plainly show that the prothrombin concentration in the blood of the babies studied was essentially the same as that of normal adult blood. It was found, however, that the prothrombin diminished in infants' blood more rapidly than from that of adults, and curiously in a few bloods, such as Case 3, the decrease of prothrombin was strikingly rapid when the plasma was diluted.

These findings are completely at variance with those reported by Brinkhous, Smith and Warner. 2 In their series the prothrombin concentration of the bloods of the 3 babies who were less than 11 days old were 27, 36, and 44% of normal. Furthermore, even in infants 2 months old, they found that the prothrombin was less than

50% of the adult level. In view of the exceedingly low incidence of hemorrhage in very young infants, such low prothrombin values seem rather surprising. It must be remembered that the methods of both Smith and Quick are empirical and based on certain unproved assumptions. Smith and his coworkers take for granted that high dilution of plasma does not alter the prothrombin, but does inactivate the normal antithrombin.