Low total protein S antigen but high protein S activity due to decreased
C4b-binding protein in neonates
HP Schwarz, W Muntean, H Watzke, B Richter and JH Griffin
Second Department of Internal Medicine, University of Vienna, Austria.
Protein S, a vitamin K-dependent cofactor for activated protein C, exists
in normal adult plasma in a free anticoagulantly active form and in an
inactive form complexed to C4b-binding protein. Immunologic and functional
levels of protein S and C4b-binding protein in plasma were determined for
20 newborn infants and compared with adult normal pooled plasma. Total
protein S antigen levels averaged 23%, similar to other vitamin K-dependent
plasma proteins. However, the protein S anticoagulant activity was 74% of
that of adult normal plasma. This apparent discrepancy of activity to
antigen was shown to be due to low or undetectable levels of C4b-binding
protein, which results in the presence of most if not all of protein S in
its free and active form. The relatively high level of anticoagulantly
active protein S in infants may enhance the potential of the protein C
pathway, thereby minimizing risks of venous thrombosis in this group.
Volume 71,
Issue 3,
pp. 562-565,
03/01/1988
Copyright © 1988 by The American Society of Hematology
