Protein C, Protein S

Last updated: Friday, 02, April, 2004

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Item Process

4.5 mL blood added to 0.5 mL citrate.


Functional or immunoassay.

Reference Interval

Typically around 60-120% of the activity in pooled normal control plasma.


Investigation of tendency to venous thromboembolism; recurrent, unexplained, or with positive family history.

There is some overlap between deficiency states and the normal range.

Levels are reduced by oral anticoagulant therapy and specimens should be collected before warfarin is commenced.


Not all individuals with proven deficiency develop venous thrombosis.

These proteins are vitamin K dependent, natural inhibitors of coagulation.

Acute severe deficiency of protein C in association with loading doses of oral anticoagulants has been incriminated in the pathogenesis of warfarin induced skin necrosis.

These proteins, particularly protein S, may fall during pregnancy.

Abnormal test results should always be repeated for confirmation and to exclude test or collection artefacts  - consult laboratory.


Clouse LH and Comp PC. N Engl J Med 1986; 314: 1298-1304.

Kessler CM and Strickland DK. Clin Chim Acta 1987; 170: 1-36.