Endocrine Abstracts

Background: Hyperthyroidism is associated with reduced neutrophil counts. Whether thyroid autoimmunity (TSH-receptor antibodies; TRAb) modifies the relationship between free thyroxine (FT4) and neutrophils, and how ethnicity relates to neutrophil levels at diagnosis, remains unclear.

Methods: Results from 237 adult patients with newly diagnosed hyperthyroidism with diagnostic thyroid function tests and TRAb titre between August 2020 to July 2025 were retrospectively analysed. A univariate general linear model (ANCOVA) was used to assess the effects of FT4 and TRAb on neutrophil count, including their interaction. Low absolute neutrophil count (ANC) was defined as <2.0×10⁹/l. Neutrophil counts and neutropenia rates between Graves’ disease (GD) (elevated TRAb) and non-GD, across self-identified ethnic groups, were compared.

Results: Of 237 patients, 152 had Graves’ and 85 had non-Graves’ aetiologies. Neutrophil counts were lower in Graves’ (median [IQR] 3.44 [2.67–4.64]×10^9/l) than non-Graves’ hyperthyroidism (3.71 [2.92–5.12]×10^9/l; P = 0.045).The TRAb×FT4 interaction was significant, indicating that the association between FT4 and neutrophils differed by TRAb level (P < 0.001). Higher FT4 was linked to disproportionately lower neutrophils in patients with high TRAb, with little FT4 effect in TRAb-negative patients. Ethnicity was an important determinant of neutrophil count: Black GD patients had higher prevalence of low ANC (33.3%) than Asian (10%) and White patients (2.5%, P < 0.001). Mean ANC in GD was 1.14 x10⁹ higher upon achieving euthyroid status than at diagnosis (P = 0.002). Seven individuals continued to have low ANC (5 of Black ethnicities, 1 White, 1 unspecified) and two remained neutropenic (both of Black ethnicities).

Conclusions: Both autoimmunity and ethnicity significantly influence neutrophil counts in newly diagnosed hyperthyroidism. Patients with high TRAb and high FT4 exhibited the greatest neutrophil reductions. Neutrophil counts and neutropenia risk vary by ethnicity, with Black patients disproportionately affected – perhaps reflecting thyrotoxic effect superimposed on the benign ethnic neutropenia. Our findings support individualised interpretation of neutrophil counts in hyperthyroid patients.