Differential Diagnosis

Presence of factor V Leiden (can be heterozygous or homozygous)

Presence of prothrombin 20210 mutation (can be heterozygous or homozygous)

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Presence of antiphospholipid antibody; could be manifested as lupus anticoagulant or anticardiolipin antibodies or anti-beta 2 glycoprotein 1 antibodies (IgG, IgM, IgA)

Elevated homocysteine

Deficiency of protein C not produced by Coumadin or other acquired cause

Deficiency of protein S not produced by Coumadin or other acquired cause

Deficiency of antithrombin not produced by heparin or low-molecular-weight heparin therapy or other acquired cause

Suggested Additional Lab Testing

Test for activated protein C resistance as a screening test for factor V Leiden mutation.

If screening test suggests a heterozygous or homozygous form of factor V Leiden mutation, perform a genetic test to determine zygosity.

If lupus anticoagulant is present, the activated protein C resistance test will suffer interference; only the genetic test for factor V Leiden should be performed in this circumstance.

Perform genetic test for prothrombin 20210 mutation; there is no simple screening test for this abnormality.

Test for antiphospholipid antibody, both for lupus anticoagulant and anticardiolipin antibodies, and/or anti-beta 2 glycoprotein 1 antibodies (IgG and IgM at least).

Test for protein C functional activity; if the functional activity is low, test for protein C antigen to reveal type of protein C deficiency.

Test for protein S either by functional assay or free antigen assay; if there is a deficiency, measure total protein S antigen to type a congenitally low protein S patientt. Test for antithrombin functional activity; if it is low in absence of heparin, measure antithrombin antigenic activity to type the deficiency.