Protein C activity

Protein C and protein S usually indicate adequate clotting regulation. Low protein C or protein S level or activity indicates blood clotting is not sufficiently regulated and there is an increased risk of developing a clot that blocks the flow of blood in the veins.

- Sample type:

Specimen Type:

Platelet-poor plasma

Collection Container/Tube: Light-blue top (3.2% sodium citrate)

- Uses:

Provides important control of blood coagulation by regulating the activities of factor VIIIa (FVIIIa) and factor VA (FVa), cofactors in the activation of factor X and prothrombin, respectively.

- Precaution:

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

2. Heparin (unfractionated or low molecular weight) 2 U/mL or more may interfere with this assay.

- Interfering factors:

Activated protein C (aPC) is a natural anticoagulant due to its actions that proteolytically inactivate clotting factors VA and VIIIa. APC is generated after an interaction of protein C with thrombin, bound to the endothelial cell surface protein thrombomodulin.

- Pre analytical errors:

1) Sample collection

2) Needle size,

3) Collection tubes

4) Sample delivery to the laboratory

- Corrective action:

(i) For complete instructions, see Coagulation Guidelines for Specimen Handling and Processing. Centrifuge, transfer all plasma into a plastic vial, and centrifuge plasma again.

(ii) Aliquot plasma into a plastic vial leaving 0.25 mL in the bottom of centrifuged vial.

(iii) . Freeze plasma immediately (no longer than 4 hours after collection) at -20 degrees C or, ideally, at < or =-40 degrees C.

- Post analytical errors:

a) Evaluation of test results

b) Decision to release test results

c) Preparation of the laboratory test report

d) Release of the laboratory test report

e) Reporting of test results

- Reference rang:

The normal range of protein C activity in healthy adults is between 65 to 135 IU dL-1. Patients with mild protein C deficiency have activity levels between 20 IU dL-1 and the lower limit of normal values, as determined by age.