
Protein S Activity Functional









The Protein S Activity Functional test measures the activity of protein S, a natural anticoagulant protein in the blood. It helps evaluate the risk of abnormal blood clot formation (thrombosis) and is commonly used in the workup of unexplained clotting disorders.












Understanding Protein S Activity Functional
Protein S is a protein in the blood that depends on vitamin K and helps control blood clotting. It supports activated protein C, which stops blood from clotting too much by inactivating certain clotting factors. If protein S is low or not working properly, it can cause harmful blood clots, leading to conditions like deep vein thrombosis, pulmonary embolism (clots in the lungs), or repeated miscarriages in women.
The Protein S Activity Functional test is often recommended for those with unexplained or repeated blood clots, recurrent miscarriages, or a family history of clotting problems. It can also help identify whether protein S deficiency is inherited or acquired due to conditions such as liver disease, pregnancy, certain infections, or the use of medications like warfarin. By measuring protein S activity, this test provides important information for diagnosing clotting disorders and planning management (e.g., anticoagulation decisions) with a doctor.
For the Protein S Activity Functional test, with prior approval from the treating doctor, discontinue heparin 1 day before and oral anticoagulants 7 days before the test, as these medications can interfere with test results. A completed coagulation requisition form (Annexure - CR/05) is required for sample collection. While overnight fasting is preferred, it is not mandatory. Additionally, please provide complete clinical details along with the medication history or a doctor’s prescription, as this information is vital for proper interpretation of the test results.
Test result ranges are approximate and may differ slightly between labs depending on the methodology and laboratory guidelines. Do not self-medicate and always consult a doctor to understand the test results correctly.
Please note: This is an outsourced test. The sample is collected by TATA 1MG and processed at a NABL accredited partnered lab.
What does Protein S Activity Functional measure?
The Protein S Activity Functional test measures the functional activity of protein S in regulating blood clotting.
- Low functional protein S activity suggests protein S deficiency (inherited or acquired), increasing the risk of abnormal clot formation.
- Normal activity suggests that protein S function is adequate.





FAQs related to Protein S Activity Functional
- Gupta A, Tun AM, Gupta K, et al. Protein S Deficiency. [Updated 2022 Dec 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from:
- Practical Haemostasis. Protein S Assays. Practical‐Haemostasis.com. [Accessed 20 Aug. 2025]. Available From:
- Majumder R, Nguyen T. Protein S: function, regulation, and clinical perspectives. Curr Opin Hematol. 2021 Sep 1;28(5):339-344. [Accessed 20 Aug. 2025]. Available From:
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