Protein
S
Definition:
Protein S is a vitamin K dependent
protein which is found in two forms in the peripheral
blood:
An ELISA assay based on an antibody
to protein S which forms a complex patient protein S. An anti-protein S conjugated with peroxidase is added
which binds with antibody-protein S complex. This complex then reacts with substrate to form a colored
complex.
40% as free protein S
which acts as a cofactor with APC to neutralize Va and VIIIa
Principle of test:
60% as bound protein S
which is bound with C4bBp (a C4b binding protein)