Venous thromboembolism (VTE) incidence is rising rapidly in Japan with lifestyle westernization and aging. Deficiency of
protein S, an important blood coagulation regulator, is a risk factor for VTE.
Protein S deficiency prevalence in Asians is approximately 10 times that in Caucasians and that of
protein S type II deficiency, associated with the
protein S Tokushima mutation (K155E), is quite high in Japan. However, currently available methods for measuring
protein S are not precise enough for detection of this deficiency. We developed a novel assay system for precise simultaneous determinations of total
protein S activity and total
protein S antigen level, using a general-purpose automated analyzer, allowing
protein S-specific activity (ratio of total
protein S activity to total
protein S antigen level) to be calculated. Mean specific activity was 0.99 for samples from healthy individuals but 0.69 or less (mean-3SD) in
protein S type II-deficient and
warfarin-treated samples, but was 1.0 in an
estrogen-treated sample with significantly decreased
protein S antigen.
Protein S gene analyses in healthy individuals with specific activity 0.69 or less revealed the K155E mutation in all three. These results show our new assay system to be an effective screening tool for
protein S type II deficiency. This system can also be used in an automated analyzer, facilitating numerous sample measurements, and is, thus, applicable to regular medical checkups and diagnosing VTE. Such applications would potentially contribute to early detection of
protein S type II deficiency, and, thereby, to
thrombosis prevention.