Analytical and Clinical Validation of a Remote Laboratory Test for Prothrombin Time and INR Determination in Patients with Antiphospholipid Antibody Syndrome and Systemic Lupus Erythematosus.

Antiphospholipid syndrome (APS) is an autoimmune disorder associated with antiphospholipid antibodies, leading to coagulation imbalance, thrombosis, and obstetric complications. It may occur as a primary condition or in association with systemic lupus erythematosus (SLE). Patients with APS often require long-term anticoagulation therapy, monitored by prothrombin time (PT) expressed as international normalized ratio (INR). Remote laboratory testing (RLT) devices may improve monitoring by providing faster and more convenient results; however, their accuracy in APS patients remains uncertain. This study aimed to validate a rapid and portable device (bSens.INR) for PT/INR measurement in patients with APS and SLE receiving warfarin, compared to a control group without these conditions. Accuracy, repeatability, and agreement with the standard laboratory method were evaluated according to established guidelines. A total of 40 PT/INR measurements were obtained using the bSens.INR and 20 using the standard method. Overall concordance was 77.5%, with lower agreement in APS/SLE patients (60%) compared to controls (95%). Approved results showed 100% repeatability. A strong positive correlation was observed between methods (Spearman r = 0.80, p < 0.0001), while Bland-Altman analysis indicated a bias of 0.26 INR units. The presence of antiphospholipid antibodies appears to interfere with PT/INR measurements obtained by the bSens.INR, reducing accuracy in APS and SLE patients. Although the device shows promising performance, its use in autoimmune populations should be approached with caution, reinforcing previous findings on the limitations of RLT in these conditions.