Coagulation Test Names that Are Confusing

Is it Factor V or Factor V Leiden?

Factor V is rarely ordered

· The most common purpose for ordering the factor V activity assay is to help with the differential diagnosis of liver disease.

· The factor V assay is also ordered to establish the presence of an inherited factor V deficiency. These are very rare and are associated with severe bleeding in infancy.

Factor V Leiden is ordered often

The factor V Leiden mutation is present in 3-8% of Caucasians and Hispanics and confers a 2- to 8-fold risk of thrombosis (80-fold when homozygous). The factor V Leiden mutation test is usually ordered as part of a profile that includes antithrombin (AT, ATIII), protein C (PC), protein S (PS), factor VIII (for elevated factor VIII), prothrombin 20210 mutation, and lupus anticoagulant (LAC).

When the factor V Leiden mutation assay is ordered, the laboratory first performs the activated protein C resistance (APCR) assay, which is an effective screen. The factor V Leiden mutation molecular test is only performed when the APCR ratio is less than 1.8.

Is it Factor X or Anti-Xa?

Factor X is rarely ordered

The factor X assay is used mostly to diagnose congenital factor X deficiency, a very rare disorder that causes severe bleeding beginning in infancy.

Anti-Xa is ordered often

The anti-Xa test (anti-factor Xa, or anti-activated factor X) is used to monitor heparin therapy. It may be ordered to monitor standard, unfractionated heparin when the partial thromboplastin time (PTT) cannot be used, such as when the patient has the lupus anticoagulant. The anti-Xa test is the only test that works for monitoring low molecular weight heparin such as LovenoxÒ or FragminÒ, or synthetic heparin such as DanaparoidÒ.

For more information contact the UAB special coagulation laboratory at 205-934-8650.