This algorithm is intended for use with additional UpToDate content on protein S deficiency.
VTE: venous thromboembolism. * Protein S levels in the general population vary widely. The lower limit of normal depends on the assay, the clinical setting, and the age of the patient. Levels of total or free protein S antigen <60 to 65 international units/dL in an individual with a VTE or a strong family history suggest deficiency. Levels of free protein S <33 units/dL are predictive of increased VTE risk in an individual with a first VTE and a negative family history. Interpretation of a specific result should be based upon the reference range reported by the laboratory. ¶ Obtain hematology consultation to assist in the interpretation of abnormal test results and to guide further evaluation.
