ExtractFibrinogen and factors V, II, and VII + X assays were performed by micromethod on days 1, 2, 3, and 10 of life in 96 premature infants ( <37 weeks gestational age). "Sick" premature infants, mainly with respiratory distress syndrome, were compared with premature infants considered to be thriving. In the thriving infants, the mean level of the studied clotting factors appears to be independent of gestational age. Fibrinogen and factor V levels are correlated in thriving as well as in sick infants; both are significantly decreased in the sick infant group. In both groups, factors //and VII + Xlevels were consistently low on the 1st day of life. They progressively increased but did not reach adult levels by the 10th day of life despite routine vitamin K x administration. Overall mortality as well as clinical hemorrhagic manifestations were closely related to blood clotting factor levels. Pathologic and biologic data indicate a relation between coagulation abnormalities in premature infants and the occurrence of disseminated . intravascular clotting. SpeculationIt can be postulated that low levels of blood clotting factors result from either diminished production (immaturity, toxicity, etc.) or increased utilization or consumption (i.e., disseminated intravascular coagulation (DIG)). Hypercoagulability and disseminated intravascular coagulation have been described in premature infants, especially in those with respiratory distress. By means of microtechnics, it is now possible to study the evolution of blood clotting factor levels in premature infants with and without respiratory distress in an attempt to better understand the relation of blood clottinglevels and the presence of DIC. Introductionlarly useful for analysis of the rapid changes in the

SummaryAmidolytic assay of antithrombin III on capillary blood can validly substitute for similar assays performed on venous blood, as an excellent correlation exists (r = 0.95).For the amidolytic assays of heparin cofactor activity, a much less satisfactory correlation is found (r = 0.81). Results are far more dispersed and a decrease is observed in late capillary samples.Using a low heparin concentration to assay heparin cofactor activity leads to surprisingly high activities for capillary blood. The same type of discrepancy is observed during the earliest stages of clotting of venous blood.