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The online version of this article has a Supplementary Appendix. BackgroundInherited deficiency of antithrombin, protein C and protein S, three important, naturally occurring coagulation inhibitors, might play a major role in the occurrence of venous thromboembolism in Chinese. The establishment of age-and gender-related normal ranges of these inhibitors is crucial for an accurate diagnosis of these deficiencies. Design and MethodsWe designed a prospective cross-sectional study recruiting healthy adults from four universityaffiliated hospitals in China. Antithrombin, protein C and protein S were studied by measuring their activity. Gene analysis was performed when natural anticoagulant deficiency was suspected. Polymorphisms of the factor V gene were searched for among subjects who were positive for activated protein C resistance. ResultsIn 3493 healthy Chinese adults (1734 men, 1759 women; age 17-83 years), we found higher age-adjusted activities for protein C and protein S in men than in women but no sex difference for antithrombin. In women, mean protein C and protein S activities increased with age. In men, mean protein C levels increased with age up to the age of 49 but decreased after 50 years old; mean protein S levels decreased after 50 years of age. Antithrombin levels remained stable over time in women but decreased significantly after 50 years of age in men. Reference values according to age and sex allowed the identification of 15 genetic variants (protein C: 10, antithrombin: 3, protein S: 2) in subjects with protein activity below the 1 st percentile. ConclusionsThis is the largest survey ever conducted in the healthy general Chinese population. These normal ranges provide the essential basis for the diagnosis and treatment of thrombosis in Chinese.Key words: antithrombin, protein C, protein S, normal ranges, genetics, Chinese. Citation: Zhu T, Ding

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