In a nonpregnant state, protein S deficiency is indicated by a free protein S antigen level of:

In a nonpregnant state, a free protein S antigen level of less than 55% is considered indicative of protein S deficiency. Protein S is a crucial anticoagulant protein that plays a key role in the regulation of coagulation by serving as a cofactor to protein C in the inactivation of factors Va and VIIIa. When protein S levels drop below the threshold of 55%, it suggests an increased risk of venous thromboembolism due to diminished anticoagulant activity.

In clinical practice, evaluating protein S levels helps in diagnosing thrombophilic states when patients present with thromboembolic events. The reference ranges for free protein S antigen can vary, but a level under 55% is generally accepted as a marker for potential deficiency and carries clinical significance. Understanding these thresholds assists healthcare professionals in making informed decisions regarding the management of patients who may be at risk for thrombosis.