Acta bioquímica clínica latinoamericana
versión On-line ISSN 1851-6114
Protein S has an essential anticoagulant function acting as activated Protein C cofactor and forming an equimolecular complex with it. In the presence of calcium this complex regulates the coagulation process inactivating thrombin activated factors V and VIII by proteolysis. In plasma there are two different forms: a) free Protein S which acts as the cofactor of activated protein C (representing about 40% of total Protein S) and b) C4-BP(C4 binding protein) bound protein S which exhibits no activity as cofactor of activated Protein C (representing about 60% of total PS). The objetive was to compare the PS dosage determination by two methods: immunoturbidimetric and clotting, and to investigate how pre-analytical variables affect the results. The following results were obtained: Clotting method: CV intra assay: (n=20): 4%, CV interassay (n=20, 3 days): 3.4%; immunoturbidimetric method CV intra assay (n=20): 3.7%: CV inter assay (n=20.3 days): 4.5%. There is a good correlation (R2 = 0.94) between both methods; when the clotting method is calibrated in batch with the samples. There is significant difference between fresh and frozen ( -20 °C and -80 °C) samples when the latter have been desfrozen only once.
Palabras clave : Protein S; Free protein S; Prenalytical variables.