Tests available for patients on direct oral anticoagulants (DOACs) - anti-Xa assays
Principle
- A chromogenic functional assay of factor Xa inhibition
- Patient plasma + known excess FXa + antithrombin (in some kits) + chromogenic substrate
- Residual FXa cleaves the substrate -> colour
- Colour is inversely proportional to drug effect
- The result is only meaningful against the right calibrator
| Calibrator | Reports |
|---|---|
| LMWH (enoxaparin) | anti-Xa IU/mL |
| UFH | anti-Xa IU/mL (different range) |
| Danaparoid, fondaparinux | drug-specific |
| DOAC-specific (apixaban, rivaroxaban) | ng/mL drug concentration |
- A "heparin" anti-Xa run on an apixaban sample gives a number that is qualitative at best - it confirms drug presence, not concentration
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