Department of Haematology


  • For Protein S testing as part of a full Thrombophilia screen, please see the Thrombophilia Screen test page.
  • Test performed at GRH

Protein S (PTS) is a Vitamin-K dependant factor which serves as a cofactor for activated Protein C in the degradation of Factors V and VIII. It circulates in blood plasma in both free and bound (to C4b binding protein) forms. Only the free portion has activity. Inherited PTS deficiency can account for recurrent thrombo-embolic episodes in young adults. Most cases are heterozygous. Acquired PTS deficiency can occur with Vitamin K deficiency, Oestroprogesterone therapy, oral anticoagulation therapy, liver disease, DIC, the third trimester of pregnancy, and in the early post-operative phase.

Sample Requirements

For Protein S analysis alone:

3ml or 3.5ml Trisodium Citrate sample

3ml Trisodium citrate

Sample Storage and Retention

  • Pre analysis storage: do not store, send to laboratory within 2 hours.
  • Sample retention by lab: Citrate samples are retained for a minimum of 24 hours at 15-30°C. If specialist coagulation tests are requested, one or more aliquots may be frozen until analysis (or up to two months) at between -15 and -40°C. After analysis, these samples will be retained for a further 24 hours at 15-30°C.

This test can be added on to a previous request as long as there is sufficient sample remaining and the sample is less than 4 hours old.

Turnaround Time

Protein S testing only: within 4 weeks

Reference Ranges

Test Reference Range Units
Total Protein S 62 - 156 %
Free Protein S (adult male) 72 - 123 %
Free Protein S (adult female) 55 - 124 %