Department of Haematology


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

Protein C (PTC) is a Vitamin K dependant factor which, after activation by Thrombin, acts with it's co-factor Protein S to degrade the activated forms of Factors V and VIII. Inherited PTC deficiency accounts for 5-7% of recurrent thrombo-embolic episodes in young adults. Deficiency can be the result of a defect at the substrate binding site (qualitative, Type II deficiency) or as a result of reduced levels of otherwise normal PTC (quantitative, Type I deficiency). Most cases are heterozygous, but some homozygous cases have been described in neonates with massive visceral thrombosis and purpura fulminans. Acquired PTC deficiency can be found in Vitamin K deficiency, oral anticoagulation therapy, liver disease, DIC and in the early post-operative phase.

Sample Requirements

For Protein C 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 C testing only: within 4 weeks

Reference Ranges

Result Reference Range Units
Protein C Activity 70 - 140 %
Protein C Antigen 62 - 143 %