Intravascular hemolysis and multitreatment predict thrombosis in patients with autoimmune hemolytic anemia

BACKGROUND: Thrombosis may complicate autoimmune hemolytic anemia (AIHA), but its predictors are still lacking, and no clear‐cut indications for anticoagulant prophylaxis are available. OBJECTIVES: To characterize frequency and severity of thromboses in AIHA patients and identify risk factors for thrombosis that may advise primary anticoagulant prophylaxis. PATIENTS/METHODS: A total of 287 consecutive AIHA patients diagnosed and followed from 1978 at a tertiary Italian center were retrospectively studied; 174 of them were prospectively evaluated from January 2020 until December 2021. AIHA relapse, thrombosis occurrence, and primary anticoagulant prophylaxis were evaluated. RESULTS: Thirty‐three AIHA patients (11.4%) experienced thrombosis, 70% of whom hospitalized. The cumulative thrombosis incidence was higher in patients with lactate dehydrogenase (LDH) ≥ 1.5 (hazard ratio [HR] 3.22), in those experiencing infections (HR 3.57), receiving transfusions (HR 3.06), rituximab (HR 3.3), or cyclophosphamide (HR 2.67). By multivariable analysis, LDH, transfusions, rituximab, and cyclophosphamide treatment emerged as independent factors associated with thrombosis. Among 174 patients prospectively followed in the past 2 years, we observed 70 acute hemolytic episodes in 45 patients; 33/45 displayed LDH ≥1.5 × upper limit of normal, and 17 received anticoagulant prophylaxis with low molecular weight heparin for a median of 70 days (30–300). In those receiving prophylaxis no thrombotic complications occurred, whereas five thrombotic episodes were registered in the remaining 16 cases. CONCLUSIONS: Thrombosis was observed in about 11% of AIHA patients, mainly grade 3, and associated with intravascular hemolysis, need of transfusions, multitreatment, and infections, advising primary anticoagulant prophylaxis in these settings.