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A man with recurrent DVTs is found to have elevated prothrombin levels. Genetic testing reveals the prothrombin G20210A variant.
AD; F2 c.*97G>A (legacy "G20210A"; 3' UTR variant)
- ~2% carrier frequency in Caucasians
- Elevated prothrombin levels
- 2-3x increased risk of VTE
- Often co-inherited with Factor V Leiden
- Targeted F2 genotyping for the G20210A variant (the diagnostic test; DNA-based, unaffected by acute thrombosis or anticoagulation)
- Plasma prothrombin (factor II) activity may be elevated but is not specific or diagnostic
- Often ordered alongside Factor V Leiden testing in a thrombophilia workup
- Treat acute VTE with standard anticoagulation; the variant does not change initial therapy
- Duration of anticoagulation is driven by the clinical event (provoked vs unprovoked, recurrence), not by the genotype alone
- No prophylactic anticoagulation for asymptomatic heterozygous carriers; counsel on situational risk (surgery, immobility, estrogen-containing contraceptives, pregnancy)