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

## TL;DR

A patient with Graves disease and a Duffy-null blood type was safely treated with standard medication despite having low neutrophil counts.

## Contribution

This case highlights that the Duffy-null phenotype does not increase infection risk and should not delay antithyroid drug treatment.

## Key findings

- A patient with the Duffy-null phenotype had baseline neutropenia but no increased infection risk.
- Antithyroid drugs can be safely administered to Duffy-null individuals without dose adjustment.
- Baseline blood tests are recommended before starting antithyroid drugs in such patients.

## Abstract

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.