Protein S Activity
(Protein S)

Protein S is a Vitamin K depended protein, synthesized in the liver. It acts in the body as a natural anticoagulant. As co-factor of activated Protein C, it triggers the inactivation of the clotting factors VA and VIIIa.

Sample type:

Specimen Frozen plasma Na citrate (Light Blue top tube)

Uses:

• To help investigate the cause of a blood clot (thromboembolism), such as a deep vein thrombosis (DVT) or pulmonary embolism (PE); to determine whether you may have a protein C or protein S deficiency.

• Sometimes, this test is done to find the cause of repeated miscarriages.

Precautions:

• Anticoagulated a 5-mL venous blood sample with sodium citrate (blue-topped tube).

• centrifuge, transfer all plasma into a plastic vial, and centrifuge plasma again.

• Aliquot plasma into a plastic vial leaving 0.25 mL in the bottom of centrifuged vial.

• Freeze plasma immediately (no longer than 4 hours after collection) at -20° C or, ideally, at ≤-40° c.

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

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

Interfering factors:

• Protein S acts as a cofactor for the serine protease Activated Protein C [APC] in the inactivation of Factors VA and VIIIa.

• A lack (deficiency) of protein S can lead to excess clotting. These clots tend to form in veins, not arteries.

• A protein S deficiency may be inherited. It can also develop due to pregnancy or certain diseases, including:

• Disorder in which the proteins that control blood clotting become over active (disseminated intravascular coagulation)

• HIV/AIDS infection

• Liver disease

• Long-term antibiotic use

• Warfarin (Coumadin) use

• Protein S level rises with age, but this does not cause any health problems

Pre analytical errors:

• wrong patient preparation

• Improper tube

• clotted sample

• overfilled tube

• underfilled tube

• sample received more than 24 hrs after collection

• mislabeled or unlabeled specimen

corrective action:

• Enquiry before sample collection

• Appropriate tube is selected

• Follow proper order of draw

• Blood samples are mixed properly

• Care is taken during blood collection

• Patient’s name with laboratory no

Post analytical errors:

• Incorrect reference values

• Physician not notified of a panic or critical value

• Incorrect interpretation of lab results by physician

• Incorrect data entry of lab result

Reference range:

The reference range for Protein S are:

Males >70-140 U/dL.

Females >60-130 U/dl.

Protein S levels are low at birth [as are all the Vitamin K dependent clotting factors] and do not reach adult values until approximately 6 months of age.