Role of lupus anticoagulants in immediate acting inhibitor positivity in congenital haemophilia A patients.

Objectives: Presence of lupus anticoagulants (LA) in haemophilia and their interference in coagulation assays is well-known. Factor VIII (FVIII) inhibitors are generally time and temperature dependent whereas LAs are immediate acting inhibitors (IAIs). The present study reports the challenges in laboratory detection of both progressive and non-progressive, specific FVIII inhibitors in the presence of LA.

Methods: From 2012 through 2015, 4900 HA patients were screened for inhibitors. APTT based inhibitor screening tests and Nijmegen-modified Bethesda assay (NBA) were done in all samples. LA test and FVIII inhibitors by ELISA were done in patients with IAIs.

Results: Out of 451 patients positive for inhibitors in the initial screening tests, classical and progressive FVIII inhibitors were observed in 398 patients while 53 had IAIs showing no/partial correction in 1:1 mixtures of NPP and patient plasma. In 27 patients, both FVIII and FIX activity levels were <1%, resulting in difficulty in diagnosis. In 48 HA patients with IAIs, 42 were LA positive. 4 patients were found to have only LA with false positive results in NBA while 38 had a combination of LA and FVIII inhibitors. Six patients were LA negative and had only FVIII IAIs. Five (62.5%) of 8 HA patients initiated on immune tolerance induction (ITI) also were positive for IAIs.

Conclusion: The findings emphasizes the presence of specific FVIII inhibitors in congenital HA with absence of time dependent inactivation kinetics in a small proportion of cases. ELISA or chromogenic assays along with LA testing can offer accurate laboratory diagnosis in patients with coexisting LA.