Coagulation Panel Updated Apr 17, 2026

Protein C

Protein C is a vitamin K–dependent protein found in blood that helps regulate clotting. On a Protein C on a blood test or Protein C on a lab report, the result shows how much of this clot-regulating protein is present or active. The Protein C test is usually part of a coagulation panel and is read alongside other clotting markers.

What Is Protein C?

Protein C is a blood protein involved in clot regulation. A Protein C test measures how much of this protein is present or how well it functions, depending on the lab method used. Protein C on a lab report reflects part of the body’s clot-control system rather than red cell content. In many reports, Protein C is discussed in units such as % or IU/dL, depending on the assay.

Why Is Protein C Tested?

Protein C is commonly measured in a coagulation panel, sometimes as part of a broader blood-clotting workup. The Protein C test helps describe clotting balance by showing whether the Protein C level is within the Protein C normal range. Protein C on a blood test is often interpreted together with other clot-related values, rather than by itself. In some reports, Protein C may also be ordered with tests such as protein S, antithrombin, PT/INR, and aPTT.

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Protein C Normal Range

Group Range Unit
Adult Male 70–150 %
Adult Female 70–150 %

Reference ranges may vary by laboratory and individual factors.

What Does High Protein C Mean?

A high Protein C test result usually means the measured Protein C level is above the Protein C reference range for that lab. In many methods, values above about 150% may be flagged as high Protein C, though cutoffs vary by assay. High Protein C does not describe a specific disorder on its own; it usually reflects variation in clot-regulating protein levels or test method. On a Protein C on a lab report, the key point is how far the value sits above the lab’s stated range.

Associated factors

Recent vitamin K intake — Protein C depends on vitamin K, so intake changes can shift the measured level.
Pregnancy — normal blood-volume and clotting changes can move Protein C upward in some people.
Estrogen-containing medications — hormone exposure can alter clot-related protein measurements.
Recent exercise — temporary fluid shifts can concentrate circulating proteins and affect Protein C.
Dehydration — lower plasma volume can make Protein C appear high on a lab report.
Laboratory method differences — activity assays and antigen tests may report different Protein C values.
Age-related variation — Protein C can vary across life stages and may sit higher in some adults.
Smoking — tobacco exposure can influence clotting protein balance and Protein C measurements.

What Does Low Protein C Mean?

A low Protein C test result means the measured level is below the Protein C normal range used by that lab. In some assays, values below about 70% may be considered low Protein C, but the exact cutoff depends on the method. Low Protein C on a blood test can reflect less protein being present or less protein activity being detected. On a Protein C on a lab report, low values are interpreted with the assay type, the reference interval, and related clotting markers.

Associated factors

Low vitamin K intake — Protein C depends on vitamin K, so limited intake can reduce measured levels.
Liver function changes — Protein C is made in the liver, so reduced production can lower the value.
Warfarin-type medication use — these medicines reduce vitamin K–dependent proteins, including Protein C.
Recent major blood loss — loss of circulating proteins can temporarily lower Protein C.
Inflammation or recent illness — temporary shifts in clotting proteins can change the Protein C test result.
Inherited variation — some people have naturally lower Protein C activity from family traits.
Laboratory handling issues — delayed processing or sample problems can affect Protein C measurement.
Dilution from IV fluids — extra fluid in the bloodstream can make Protein C appear low.

How Protein C Relates to Other Values

Protein C is read with other clotting markers on a coagulation panel, including protein S, antithrombin, PT/INR, and aPTT. Protein C on a blood test is especially useful when compared with protein S because both help regulate clot formation. PT/INR and aPTT show how long clotting takes, while Protein C shows one part of the control system behind that process. On a broader panel, these values together help describe clotting balance and blood composition.

What Factors Affect Protein C Levels?

Protein C can vary with age, sex, hormones, hydration, and recent exercise. Time of day, recent diet, and pregnancy can also shift the Protein C test result slightly. Different laboratories may use different methods, so the Protein C normal range can vary from one report to another. Altitude, smoking, and temporary fluid changes may also influence Protein C on a lab report. Because of this, the same Protein C value can be read differently across labs and collection conditions.

How It Is Tested

Protein C is measured from a standard blood draw, usually from a vein in the arm. The lab may report Protein C as activity or antigen, depending on whether it measures function or amount. Common units for a Protein C test include % of normal activity or IU/dL, depending on the assay.

How to Prepare

No fasting is usually required for a Protein C test. The result is often interpreted with the lab’s Protein C reference range and the test method used.

Frequently Asked Questions

What is a normal Protein C level?
A normal Protein C level usually falls within the lab’s stated Protein C normal range, which is often around 70% to 150% for activity-based assays. The exact interval can vary by method, so the Protein C test result should be read against the range printed on the report.
What does Protein C stand for?
Protein C does not stand for a phrase in the usual lab-report sense; it is the name of a clot-regulating blood protein. On a Protein C test, the label refers to that specific protein and its measured amount or activity.
What does a high Protein C mean on a lab report?
A high Protein C means the result is above the lab’s Protein C reference range. In many reports, high Protein C reflects variation in fluid balance, hormones, vitamin K status, or assay method rather than a single named condition.
What does a low Protein C mean on a lab report?
A low Protein C means the measured value is below the Protein C normal range for that lab. On a Protein C on a lab report, low values can reflect reduced production, lower vitamin K–dependent activity, or sample and method differences.
Can hydration affect Protein C?
Yes, hydration can affect Protein C on a blood test. Dehydration may make Protein C look higher because the blood is more concentrated, while excess fluid can make it appear lower.
What is the difference between Protein C and protein S?
Protein C and protein S are both clot-regulating proteins, but they are measured as separate values on a coagulation panel. Protein C is often reviewed with protein S because the pair helps show different parts of the same clot-control system.
What unit is Protein C measured in?
Protein C is commonly reported as a percentage of normal activity (%) or sometimes in IU/dL, depending on the lab method. The unit on a Protein C test result should always be read with the reference range on the same report.
How much can Protein C change between tests?
Protein C can change modestly between tests because of hydration, recent exercise, hormones, and method differences. Small shifts may be normal, but the Protein C test result should be compared with the same lab’s Protein C reference range when possible.
Is Protein C different for men and women?
Protein C is often similar in adult men and women, but some labs use slightly different reference intervals or note hormonal variation. The Protein C normal range on a report should always be checked by sex if the lab provides separate intervals.
Why is Protein C tested in a coagulation panel?
Protein C is tested in a coagulation panel because it is part of the system that helps regulate clot formation. On a Protein C on a lab report, the value adds context to PT/INR, aPTT, protein S, and antithrombin.

Disclaimer

This content is for informational and educational purposes only. It is not intended as medical advice, diagnosis, or treatment recommendation. Reference ranges may vary by laboratory. Always discuss your results with a qualified healthcare professional.

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