Comparison of protein S functional and antigenic assays in normal pregnancy.
OBJECTIVE
Our purpose was to determine the effect of pregnancy on the protein S functional assay (clot based), which is used to screen for all subtypes of protein S deficiency states, and to compare its behavior in pregnancy with antigenic assays.


METHODS
This was a cross-sectional study of 37 normal pregnant women without thromboembolic risks who were tested by both functional and antigenic protein S assays during the first, second, and third trimesters.


RESULTS
Mean protein S functional levels decline strikingly from the first to the third trimester, all 10 third-trimester patients had functional protein S levels well below the lower limit of the reference range. In contrast, only 3 of 10 third-trimester and none of the second-trimester patients had free protein S antigenic levels below the reference range.


CONCLUSIONS
The protein S functional assay should not be used in pregnancy to screen for the subtypes of protein S deficiency; misdiagnosis and inappropriate treatment could result.
Lefkowitz
J B
JB
Department of Pathology, University of Colorado Health Sciences Center, Denver 80262, USA.
Clarke
S H
SH
Barbour
L A
LA
D000293:Adolescent; D000328:Adult; D000941:Antigens / Q000097:blood*; D003169:Complement Inactivator Proteins; D003430:Cross-Sectional Studies; D005165:Factor V / Q000032:analysis; D005169:Factor VIII / Q000032:analysis; D005260:Female; D006023:Glycoproteins; D006801:Humans; D010314:Partial Thromboplastin Time; D011247:Pregnancy; D017293:Protein S / Q000032:analysis / Q000276:immunology* / Q000502:physiology*; D018455:Protein S Deficiency / Q000097:blood / Q000175:diagnosis*; D011951:Receptors, Complement / Q000097:blood; D012016:Reference Values; D013997:Time Factors
D000941:Antigens; D003169:Complement Inactivator Proteins; D006023:Glycoproteins; D017293:Protein S; D011951:Receptors, Complement; D005165:Factor V; D005169:Factor VIII