Haptoglobin is frequently low in patients with myelofibrosis: Clinical relevance

•Decreased haptoglobin can be observed in 33% of patients with myelofibrosis.•Decreased haptoglobin is not a sign of acute hemolysis or liver cirrhosis in patients with myelofibrosis.•Decreased haptoglobin is associated with high JAK2 allele burden and treatment with JAK inhibitors in patients with myelofibrosis.

A recent study, showing the absence of paroxysmal nocturnal hemoglobinuria clones in myelofibrosis, has reopened the debate around the role of decreased haptoglobin in this disease. We present here a large prospective analysis of the clinical significance of low haptoglobin in 152 patients with myelofibrosis. Low haptoglobin (<32 mg/dL) was observed in 50 patients (33%). Decreased haptoglobin did not associate with low hemoglobin levels, positive Coombs test or abnormal liver function tests, suggesting it is not result of autoimmune hemolytic anemia or liver cirrhosis. Factors strongly correlating with decreased haptoglobin were high JAK2 allele burden and ongoing treatment with JAKi. Larger scale serial measurement and longer follow-up is needed to further explain our findings.