×

Please Remove Adblock
Adverts are the main source of Revenue for DoveMed. Please remove adblock to help us create the best medical content found on the Internet.

Protein C and Protein S Blood Tests

Last updated Nov. 30, 2018

Approved by: Krish Tangella MD, MBA, FCAP

Protein C and Protein S are separate blood tests often performed together. These tests are meant, to either assess the functioning, or the abundance of these proteins.


What are the other Names for this Test? (Equivalent Terms)

  • Protein C Antigen and/or Functional Blood Test
  • Protein C, Functional or Antigen Test
  • Protein S, Functional or Antigen Test

What is Protein C and Protein S Blood Tests? (Background Information)

  • Protein C is an anticoagulant and anti-inflammatory enzyme. It requires Protein S, a coenzyme, and Vitamin K, to function. It is similar to aspirin in its “blood-thinning” effects
  • Protein C is made in the liver, while Protein S made in the inner lining of blood vessels. Both proteins circulate in the bloodstream
  • Clotting is essential to minimizing blood loss. However, like every other process in the body, it is tightly regulated. Protein C is activated during the clotting process, to keep blood clotting under control
  • Protein C exhibits its anticoagulant effects by removing the clotting factors and stimulating plasmin, a protein that degrades blood clots - a process termed as fibrinolysis
  • Deficiencies in these proteins can cause hypercoagulable blood (abnormal blood coagulation) and internal blood clotting (thrombosis). These are more commonly acquired, than are hereditary
  • There are several types of classification, characterized by Protein C and S deficiencies:
    • Type I is caused by insufficient quantity
    • Type II is caused by defective function
    • Type III (Protein S only) is caused by a low amount of active-form Protein S, but normal levels of total Protein S
  • Protein C and Protein S are separate blood tests often performed together. These tests are meant, to either assess the functioning, or the abundance of these proteins

What are the Clinical Indications for performing the Protein C and Protein S Blood Tests?

Following are the clinical indications for performing a Protein C and/or Protein S Blood Test:

  • Following a blood vessel obstruction by a free blood clot (thromboembolism), characterized by these symptoms:
    • Swelling (edema) of extremities, especially if pitting occurs
    • Tenderness
    • Deep blue color (cyanosis)
  • Whole-body inflammation (sepsis)
  • Purple skin discoloration (purpura fulminans), observed especially in infants
  • In order to differentiate inherited deficiency from acquired deficiency

How is the Specimen Collected for Protein C and Protein S Blood Tests?

Sample required: Blood

Process: Insertion of a needle into an arm vein.

Preparation required: If there is a thrombotic episode, then the test has to be performed only after a period of 10 days.

What is the Significance of the Protein C and Protein S Blood Tests Result?

Decreased Protein C and Protein S levels may indicate:

  • Serious infections
  • Kidney disorder
  • Liver disorder
  • HIV
  • Pregnancy
  • Chronic high blood pressure (hypertension)
  • Disseminated intravascular coagulation (DIC)
  • Various cancers
  • Vitamin K deficiency

Elevated Protein C and Protein S levels are rarely of any clinical concern.

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • Certain factors may interfere with the test and these include: Surgery, oral contraceptives, and chemotherapy
  • Protein C and Protein S are being considered for use in therapy for individuals with hypercoagulation or whole-body inflammation (sepsis)
  • 2-15% of Caucasians carry a genetic mutation in a clotting factor that makes it resistant to Protein C’s effects. This leads to similar symptoms as Protein C deficiency
  • Tourniquet placement for extended periods of time can cause veins to pool with blood, altering Protein C and Protein S levels and thus affecting the test results

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

References and Information Sources used for the Article:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: March 7, 2014
Last updated: Nov. 30, 2018