Management of Graves Disease With Co-Existing Duffy-Null Phenotype

Clinicians should obtain baseline white blood cell differential among those in whom antithyroid drugs (ATD) will be initiated, as patients may have neutropenia prior to initiation of ATD. We report the case of a 37-year-old male individual who had emigrated from Saudi Arabia and was found to have Graves disease. At diagnosis, the patient was leukopenic and neutropenic. Prior neutrophil counts had ranged from moderate neutropenia to normal. The patient was found to have the Duffy-null phenotype on red blood cell antigen typing, which is characterized by a clinically insignificant lower absolute neutrophil count (ANC) relative to commonly used reference ranges and no known increased risk of infection. Despite his baseline neutropenia, the patient received a standard weight-based dose of methimazole. ATD should not be withheld from patients with the Duffy-null phenotype. These patients have fewer circulating neutrophils without an increased risk of infection.