The diagnosis of Graves’s disease (GD) can be challenging in patients with atypical presentations of hyperthyroidism. Recently, TSH receptor antibody assays are proposed as first-line test for suspected GD. I here report a case of false positive TSH receptor binding inhibitory immunoglobulin (TBII) in an elderly male patient with overt hyperthyroidism caused by painless thyroiditis. This case highlights the fallacy of overreliance on TBII in making the GD diagnosis. The differential diagnosis of hyperthyroidism should not rely solely on TSH receptor antibody assays to confirm or rule out GD because false positive results are possible in patients with other causes of hyperthyroidism, like the patient reported here. Radioactive iodine uptake and scan is likely the best diagnostic test for patients with atypical presentation of hyperthyroidism.
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