Low Protein S: what it means
A Protein S result below the normal range is considered low. Here is what a reduced Protein S can point to, and when it is worth discussing with a doctor.
Reference range: ~65–140% of normal activity (lower in pregnancy and on some hormones); a natural anticoagulant that partners protein C — a LOW level (protein S deficiency) is a thrombophilia raising the risk of venous clots
Understand your full resultWhat a low Protein S can mean
- Inherited protein S deficiency — a genetic thrombophilia raising venous clot risk.
- Pregnancy — physiologically lowers protein S.
- Oestrogen — the pill or hormone therapy lowers it.
- Warfarin and vitamin K deficiency — protein S is vitamin-K-dependent.
- Liver disease, acute illness or a recent clot — can lower it.
When to discuss with a doctor
Protein S is a specialist test within a thrombophilia work-up, not a routine check. It is measured mainly after a blood clot that is unexplained, unusually severe, recurrent, in an unusual site or at a young age, or with a strong family history — to look for an inherited tendency to clot. Because pregnancy, oestrogen, warfarin, liver disease and a recent clot all lower protein S, a single low result does not by itself mean an inherited deficiency: the timing matters and the test is usually repeated away from these influences before any conclusion. A confirmed deficiency can influence treatment, prevention and advice for relatives. Mediora.AI shows protein S alongside protein C, antithrombin and D-dimer so the thrombophilia pattern is read together and reversible causes considered; confirming and acting on a low result belongs with your doctor or haematologist.
Conditions this can relate to
Keep reading
One value is a snapshot. Upload the full test to see every marker explained together.
Upload your test - freeMediora.AI is informational - interpretation, not a diagnosis. A single out-of-range value is common and often benign; always discuss decisions with your doctor.