How can Antiphospholipid Antibodies be detected in a patient who is already anticoagulated

How can Antiphospholipid Antibodies be detected in a patient who is already anticoagulated?

Measurement of aCL abs and anti-β2GPI abs are tested by ELISA and not affected by anticoagulation and can be reliably measured in a patient on heparin or warfarin. However, coagulation tests to detect LA are affected by heparin, warfarin, and DOACs, and care must be taken in determining LAs in this situation. In the patient on heparin, plasma can be treated with heparinase to remove the heparin before the coagulation tests. In a patient on warfarin, it is the PT that is primarily affected, and the aPTT is usually not prolonged. Thus, prolongation of aPTT in a patient on warfarin is still suggestive of the presence of LA. Because warfarin depletes vitamin K-dependent factors, a 1:1 mix of the patient’s plasma with normal plasma should correct the factor deficiencies induced by warfarin. Thus, if the alterations of clotting parameters are due to warfarin, the PT as well as aPTT will correct. However, as discussed earlier, a prolonged aPTT that does not correct in this situation may be indicative of LA. Patients on warfarin with significantly suppressed factor X levels (INR >2) may have a mildly prolonged dRVVT, suggesting the presence of LA. Patients must be taken off their DOAC to obtain an accurate test for LA.

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