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 also stimulates the fibrinolytic system. 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. Incident to a thrombotic event, both procoagulant and regulatory coagulation proteins may be lower than basal state due to excessive consumption or higher than basal state from reactive overproduction. Therefore, it is best not to test for Protein C deficiency during an acute thrombotic event. The Protein C antigen test determines the amount of the molecule present, not its functionality. The Protein C Chromogenic (activity) assay determines the functionality. Therefore, the Protein C Chromogenic (activity) assay is the preferred method.

Lab Testing Sections:

Coagulation (Minneapolis Campus)

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

1 – 7 days, performed on Fridays

Special Instructions:

Elective testing for Protein C deficiency is best done at least 30 days after cessation of Coumadin® therapy.

Protein C may be reduced during an acute event (thrombotic, surgical, etc.) therefore it is preferable not to test for it during this time. However a normal value at the time of an acute event excludes a congenital deficiency.


Specimen Type:

Whole blood


Light Blue top (Buffered Na citrate 3.2%) tube

Draw Volume:

2.7 mL blood in a 3 mL tube (Minimum: 1.8 mL in a 2 mL tube)

Processed Volume:

Minimum 1.8 mL (plasma)


● A clean venipuncture is essential, avoid foaming. ● Entire sample must be collected with single collection, pooling of sample is unacceptable.
● Capillary collection is unacceptable.
● Patient’s with a hematocrit level >55% must have a special tube made to adjust for the hematocrit; contact lab for a special tube.
● Mix thoroughly by gentle inversion. Deliver immediately to the laboratory at room temperature via courier or pneumatic tube.

Off campus collections:
● Must be tested within 4 hours. ● Do not refrigerate.
● If not received in our lab within 4 hours of collection, sample must be centrifuged and *platelet-poor plasma removed from cells and transferred to an aliquot tube being careful not to disturb the cell layer. Centrifuge the plasma a second time and transfer into a clean aliquot tube being careful not to include any residual platelets on the bottom of the tube. Freeze at -20°C and deliver to the lab on dry ice within 2 weeks.
*Validation of your lab’s centrifuge for platelet poor plasma is required.

Special Processing:

Lab Staff: All testing will be performed on the Mpls campus.

St.Paul Lab: Send whole blood specimens to Mpls.
For processing via courier. Must be processed within 4 hours of collection. Contact Mpls prior to sending. If there will be a delay in delivery, the sample
should be spun, plasma removed and spun again. Aliquot spun plasma into a screw-capped plastic vial and freeze at -70. Send frozen plasma.

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; underfilled tube; mislabeled or unlabeled specimens


Reference Range:


Range (%):


14 - 42%

1 - 4 days

26 - 44%

5 - 29 days

31 - 53%

30 - 89 days

32 - 54%

90 - 179 days

41 - 67%

180 - 364 days

48 - 70%

1 - 5 years

40 - 92%

6 - 10 years

45 - 93%

11 - 16 years

55 - 111%

17 years and older

70 - 140%

Critical Values:



Coumadin® will lower Protein C.

Berichrom® Protein C detects the amidolytically active portion of the activated Protein C, including the non-carboxilated molecules synthesized in vitamin K deficiency. Thus, in conditions of vitamin K deficiency, a higher Protein C activity is found with Berichrom® Protein C than when using the coagulometric method. To obtain a complete picture of a Protein C deficiency, it is therefore advisable to also use the coagulometric method of the antigenic determination technique.


Protein C in the patient sample is activated by a specific snake venom activator. The resulting Protein C(a) is assayed in a kinetic test by measuring the increase in absorbance at 405nm.


Siemens Berichrom Protein C package insert (May 2008) OUVV G15 E0501 (699), Siemens Healthcare DiagnosticsInc.,Newark, DE

Control Plasma N package insert (December 2007) Siemens Healthcare Diagnostics, Newark, DE

Control Plasma P package insert (December 2007) Siemens Healthcare Diagnostics, Newark, DE

Application Sheets for Protein C with Berichrom Protein C on BCS and BCS XP

BCS System Instruction Manual

BCS XP System Instruction Manual           

Thrombophilia Powerpoint presentation Kandice Kottke-Marchant M.D. PhD.

An Algorithmic Approach to Hemostasis Testing Kottke-Marchant (2008) CAP Press

Andrew M, Paes B, Milner R, et al, “ Development of the Human Coagulation System in the Full-Term Infant,” Blood, 1987,70(1):165-72

Andrew M, Vegh P, Johnston M, et al, “Maturation of the Hemostatic System During Childhood,” Blood,1992, 80(8):1998-2005


2/6/2012: Test moved from referral to Fairview University to being performed at Children’s Laboratory.
9/15/2014: Added Off Campus collection info.