Anaemia and thyrotoxicosis: The need to look for an alternative cause.

Abstract

Anaemia and thyrotoxicosis are both relatively common. It is unclear whether thyrotoxicosis results in anaemia in the absence of other causes. The aim of this study was to determine the prevalence and characteristics of anaemia in patients with thyrotoxicosis. A prospective cohort study of patients with thyrotoxicosis. 353 patients referred to a regional endocrinology centre in New Zealand from March 2013 to November 2014 for new-onset thyrotoxicosis. Detailed assessment including thyroid function tests, full blood count, inflammatory markers, haematological parameters and coeliac serology. Anaemia was defined as a haemoglobin value <115g/L (woman) or <130g/L (men). Anaemia was present in 31 (8.7%) patients at diagnosis. Of these, pre-existing anaemia was present in 10, and a further 11 had one or more identifiable underlying cause(s) for the anaemia. Only 10 patients (2.8% of the entire cohort) had anaemia not clearly attributable to another cause. Median free thyroid hormone levels were higher in those with anaemia of unknown cause compared to patients with thyrotoxicosis alone. The median duration of anaemia was shorter in patients with thyrotoxicosis-associated anaemia compared to those with anaemia due to an underlying cause (1 vs 6months, P=.001). In all patients with thyrotoxicosis-associated anaemia, the anaemia resolved, either prior to, or on becoming euthyroid. Anaemia coexisting with thyrotoxicosis is less common than previously reported and is mild and transient. Patients with thyrotoxicosis and significant anaemia should be investigated for other potential causes, particularly when anaemia persists.