Paroxysmal Nocturnal Hemoglobinuria is rare cause for thrombosis of the intra-abdominal veins in the ethnic Indian population - results from FLAER-based flowcytometry screening.

Background: Paroxysmal nocturnal hemoglobinuria (PNH) may present as cytopenia, hemolysis, or thrombosis at unusual sites including splanchnic vessels. Thrombosis of the portal veins and hepatic veins are associated with thrombophilic risk factors: deficiencies of protein C, protein S, and antithrombin, positivity for antiphospholipid antibodies, and factor V Leiden mutation. There is limited information regarding PNH presenting primarily as a thrombotic event. We prospectively screened 142 consecutive patients with intrabdominal thrombosis and 106 controls with fluorescently labeled inactive toxin aerolysin (FLAER)-based flowcytometry to assess the frequency of PNH as a thrombophilic risk factor in patients with intra-abdominal thrombosis.

Methods: Granulocytes of patients and controls were screened with CD 24 and FLAER and monocytes with CD 14 and FLAER. Dual negativity of >1% events in both lineages was interpreted as a positive PNH clone. Screening for thrombophilia risk factors was carried out.

Results: Two (1.4%) cases had large PNH clones. RBC also demonstrated the PNH defect. Thrombophilia risk factors were as follows: deficiency of protein S, protein C, and antithrombin in 13.4%, 4.9%, and 2.1%, respectively, and positivity for anti-beta-2 glycoprotein 1, anticardiolipin antibodies, and lupus anticoagulant in 9.2%, 1.4%, and 0.7%, respectively. Factor V Leiden mutation was seen in 1.4% patients.

Conclusion: PNH was uncommon in patients with intra-abdominal thrombosis in the ethnic Indian population. Despite low positivity, screening by flowcytometry for PNH is of value in this group of patients because it provides an opportunity to rapidly establish the diagnosis of this treatable disorder, which might otherwise be missed if the initial presentation is only thrombotic.