Abstract: A reagent is used for measuring a total protein S activity in a specimen of a patient to detect protein S abnormality. The reagent includes a first reagent containing at least activated protein C, a first phospholipid, a first surfactant, and calcium ions; a second reagent containing at least activated blood coagulation factor V, the first phospholipid, the first surfactant, and the calcium ions; and a third reagent containing at least activated blood coagulation factor X, prothrombin, a substrate of thrombin, a second phospholipid having a composition different from that of the first phospholipid, and the calcium ions. The first reagent, the second reagent, and the third reagent are prepared separately so that the first reagent, the second reagent, and the third reagent are sequentially applied to the specimen.

Abstract: A method of detecting protein S abnormalities of the invention includes the steps of: measuring an activity value of total protein S and a protein content of total protein S in a specimen, and comparing between the protein activity of the total protein S and the protein content of total protein S, which are obtained from the measurements.