Thromboblastic hyperthyroidism: Sensitive monoclonal tsh assay demonstrates suppressed immunoreactive tsh

We describe a case of frank clinical hyperthyroidism due to hydatidiform mole. This is thought to be due to human chorionic gonadotrophin (hCG) or a closely related molecule produced by the tumour. hCG can cross-react with TSH in older TSH radioimmunoassays causing falsely elevated TSH levels. We demonstrate this does not occur with a chemiluminescent immunometric (monoclonal) TSH assay despite circulating hCG levels τ106 μ/L.