Clinics and Departments

Laboratory Services

Lab Dept:


Test Name:


General Information

Lab Order Codes:



Protein C Activity Assay; Protein C Immunologic Assay

CPT Codes:

85303 – Clotting inhibitors or anticoagulants; Protein C activity

Test Includes:

Protein C activity


Test Indications:

Protein C, along with its cofactor Protein S, acts as a potent anticoagulant by destroying activated Factors 5 and 8. It is Vitamin K dependent, therefore it is decreased in coumadin therapy or Vitamin K deficiency. Protein C deficiency is a risk factor for thromboembolism. Severe deficiency may cause purpura fulminans in neonates. It is best not to test for Protein C deficiency during an acute thrombotic event. The Protein C Chromogenic (activity) assay determines amount of functional Protein C.

Lab Testing Section:

Coagulation - Sendouts

Referred to:

Fairview University Medical Center (Test# PCCH)

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

Within 2 days; test set up one to two times per week, Monday - Friday

Special Instructions:

INR is needed for interpretation (Protein C is decreased in Coumadin therapy/Vitamin K deficiency).


Specimen Type:

Whole blood


Light Blue top tube (Buffered Na Citrate 3.2%)

Draw Volume:

2.7 mL (Minimum: 1.8 mL) blood

Processed Volume:

Specimens will be processed at reference lab facility if received within 4 hours of collection. Otherwise, specimens need to be processed at referring facility and provide minimum of two 0.5 mL specimens frozen at -70. Follow directions below under Special Processing.


Do Not use the first 2 mL of blood collected.

If the patient’s hematocrit is >55%, contact laboratory to obtain a special tube.

Fill tube completely. Mix thoroughly by gentle inversion.

Special Processing:

Lab Staff: Do Not centrifuge. Do Not freeze. Send to reference lab in original Vacutainer® at room temperature if within 4 hours of collection. Forward promptly.

If specimen is >4 hours old prior to shipment, process specimen as follows:
Spin sample collected in blue top tube(s) for 5 minutes on the Stat Spin centrifuge, remove plasma and transfer to a 4 mL BCS sample cup(s), spin remaining plasma again for 5 minutes in the Stat Spin Centrifuge. Transfer plasma into two labeled 10x75 mL plastic tubes with a minimum of 0.5 mL in each. Freeze at -70 and send specimens on dry ice to Fairview University.

Patient Preparation:

If the patient is being treated with Coumadin®, this should be noted. Coumadin® will lower Protein C.

Sample Rejection:

Improper tube; clotted sample; overfilled tube; underfilled tube; lipemic sample; mislabeled or unlabeled specimens


Reference Range:


Range (%)

0 days

14 – 42%

1 day

26 – 44 %

5 days

31 – 53%

30 days

32 – 54%

90 days

41 – 67%

180 days

48 – 70%

1 years

40 – 92%

6 years

45 – 93%

11 years

55 –111%

17 years and older

70 – 170%

Critical Values:

Less than 20% (for 5 days and older)


This assay cannot be performed if the patient is receiving heparin. Heparin interferes with amyloidosis of the substrate. Lipemic samples are not acceptable. Coumadin® will lower Protein C.


Chromogenic (synthetic substrate) activity assay


Patient cannot be receiving lipids or heparin.


Fairview University Medical Center Web Page February 2014

Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis


2/25/2014: Fairview specimen processing update.
3/24/2014: Fairview reference range update.

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