Assay of protein S in systemic lupus erythematosus.
Free protein S:Ag and protein S activity determined by clotting assay are often regarded as synonymous; however, in the study group of patients, abnormal protein S activity (PS:Act) results correlated poorly with abnormal free (PS:Ag(r2 = 0.164). Significantly none of the patients in whom lupus anticoagulant and low free protein S:Ag were detected were found to have low PS:Act. These results could not be explained by activated protein C resistance, suggesting that lupus anticoagulant may cause prolongation of the clotting time within the PS:Act assay and thus give falsely high results. As reduced levels of free protein S:Ag and/or protein S activity are considered risk factors of thrombosis in systemic lupus erythematosus, these findings question the suitability of the protein S activity assay for patients who may have phospholipid antibodies.
Lawrie
A S
AS
Haemophilia Centre, St Thomas' Hospital, Guy's and St Thomas' NHS Trust, London, UK.
Lloyd
M E
ME
Mohamed
F
F
Irons
S
S
Hughes
G R
GR
Savidge
G F
GF
D017153:Antibodies, Anticardiolipin / Q000032:analysis; D000990:Antithrombin III / Q000032:analysis; D005260:Female; D006801:Humans; D016682:Lupus Coagulation Inhibitor / Q000032:analysis; D008180:Lupus Erythematosus, Systemic / Q000097:blood*; D008297:Male; D011486:Protein C / Q000032:analysis; D017293:Protein S / Q000032:analysis*
D017153:Antibodies, Anticardiolipin; D016682:Lupus Coagulation Inhibitor; D011486:Protein C; D017293:Protein S; D000990:Antithrombin III