Summary
Total and free protein S antigen and C4b-binding protein (C4bp) were determined by
rocket immuno-electrophoresis, and functional protein S was assayed by a coagulation
method, throughout pregnancy and normal puerperium and in a group of normal full-term
newborns (FTN). The functional protein S assay is based on a modification of the APTT,
using a mixture of test sample, protein S deficient plasma, activated protein C, phospholipids
and calcium. This protein S functional assay is specific for protein S since the APTT
prolongation by normal plasma was abolished by incubation of plasma with monospecific,
rabbit antiprotein S IgG. The ratios of functional protein S/free protein S antigen
in healthy men (n = 13) and women (n = 14) were 1.0 ± 0.13 (mean ± SD) and 1.03 ±
0.20, respectively. During pregnancy there is a decrease in functional protein S and
a progressive decrease in total and free protein S antigen, with a functional/free
protein S ratio of 0.75 ± 0.28 in the third trimester of pregnancy (n = 16). In early
puerperium the functional protein S level was lower than the free protein S antigen
level (ratio about 0.5). In the FTN group, the free protein S level was 39% and protein
S activity was about 70% that of adults, with a functional/free protein S ratio of
1.84 ± 0.31. C4bp values were 23.5 ± 10.3% in the FTN group, and crossed immunoelectrophoresis
showed that in this group the major protein S peak corresponded to free protein S.
These results indicate that both in early puerperium and in FTN group, free protein
S antigen may not be an adequate parameter for estimating of functional protein S
activity. The decrease in functional protein S activity during early puerperium may
be connected with the risk of developing thrombotic episodes during the postpartum
period.
Keywords
Protein S - Pregnancy - Full-term newborn - C4bp
