Factors affecting tests for thrombophilia
| Thrombophilia test | Confounding factors |
|---|---|
| Antithrombin level | Can be lower in acute thrombosis, neonatal period, pregnancy, liver disease, disseminated intravascular coagulation (DIC), nephrotic syndrome, major surgery, treatment with l-asparaginase, heparin; can be falsely negative with factor Xa inhibitors (for factor Xa-based assays), factor IIa inhibitors (for factor IIa-based assays) |
| Cardiolipin and beta-2 glycoprotein 1 enzyme immunoassays | None |
| Factor V Leiden mutation | None |
| Factor VIII level | Inflammation can raise |
| Lupus anticoagulant | False-positive result possible with heparin (if serum level > 1 U/mL), warfarin (if international normalized ratio > 3.5), direct oral anticoagulants |
| Protein C level | Can be lower in neonatal period, liver disease, DIC, chemotherapy (cyclophosphamide, methotrexate, and 5-fluorouracil combination), inflammation, acute thrombosis, treatment with warfarin or l-asparaginase; can be falsely negative with direct oral anticoagulants (clot-based assays) |
| Protein S level | Neonatal period, pregnancy (free protein S antigen levels and protein S activity levels fall during pregnancy, but total protein S antigen levels remain stable), liver disease, DIC, acute thrombosis, treatment with warfarin, l-asparaginase, or estrogens |
| Prothrombin gene mutation | None |
Based on information in references 34, 36–40.