Neutropenia in patients with hyperthyroidism: Systematic review and meta-analysis

Neutropenia, a low absolute neutrophil count (ANC), may be a sign of new-onset hyperthyroidism. The aim of this systematic review and meta-analysis was to provide the most reliable estimates of prevalence, degree and response to treatments of neutropenia in the pure hyperthyroidism setting.

A comprehensive literature search was performed in PubMed and Scopus databases for retrieving articles in English and non-English languages reporting ANC values/neutropenic cases at presentation and after therapy in patients with hyperthyroidism. A proportion meta-analysis was performed with DerSimonian and Laird method (random-effects model). Pooled data were presented with 95% confidence intervals (95% CI) and displayed in a forest plot. I² statistic index was used to quantify the heterogeneity among the studies. Sensitivity analyses for the prevalence of neutropenia and the mean of ANC in hyperthyroid patients were performed by excluding the studies without full details. Trim and fill analysis and Egger's linear regression test were carried out to evaluate the publication bias. A two-sided P-value of <.05 was regarded as significant for all analyses. The National Heart, Lung and Blood Institute Quality Assessment Tool was used to evaluate the quality of studies included.

The literature search yielded 1880 studies of which 13 studies were included for systematic review and meta-analysis. Results of the meta-analysis demonstrated that the prevalence of neutropenia in newly diagnosed and untreated patients with Graves' hyperthyroidism was 10% (CI 5%-19%, I² 88.6%) and summary mean ANC value in neutropenic was 1.4 ± 0.3 × 10⁹ /L. In all neutropenic patients under ATD therapy neutropenia resolved, thus without the worsening of the baseline ANC values or the development of agranulocytosis. The sensitivity analyses showed similar results as those of the main analyses. For all outcomes, the publication bias was not statistically significant or not calculable.

Graves' disease per se is associated with neutropenia in about 10% of cases. Neutropenia usually appears as a mild to moderate laboratory abnormality with no detectable consequences. Subnormal/mild neutropenia should not be regarded as a contraindication to use ATDs, and clinicians should know that treating hyperthyroidism they have a significant chance to normalize ANC too.