Prothrombin
(factor II)

A plasma protein that is the inactive precursor of thrombin. It is converted to thrombin by a prothrombin activator complex consisting of factor Xa, factor V, phospholipid, and calcium ions.

Sample type:

Frozen plasma Na citrate (light blue top tube)

Uses:

Evaluate an isolated prolonged PT or when there is prolongation of both the aPTT and PT and to document specific factor II deficiency

Precautions:

• Ideally the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing.

• Centrifuge the citrated blue-top tubes as soon as possible (within 60 minutes) at designated time and speed to obtain platelet-poor plasma.

• Freeze upright and transport on dry ice.

Interfering factors:

• Factor II increased in Thromboembolism

Decreased in:

• Congenital deficiency (recessive inheritance): Bleeding of various severities in homozygotes

• Acquired deficiency: Liver disease, DIC, pathologic fibrinolysis, vitamin K deficiency or warfarin therapy

Pre analytical errors:

• Severe hemolysis

• improper labeling

• clotted specimen

• specimen diluted with IV fluids

• improper sample type

• sample out of stability

Corrective Action:

• Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.

• Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio.

• The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood.

Post analytical errors:

• Result reporting

• Result interpretation

• Result distribution

Reference Range:

50 - 200 %

Note:

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples