Interpretation of thyroid function test (TFT) is often straightforward but in certain scenarios, discordance between the clinical impression and the laboratory results exists. A 50-year-old woman with a ten years history of hypothyroidism on levothyroxine presented with a recent notable change in TFT [elevated free thyroxine (FT4) and thyroid-stimulating hormone (TSH)], in an otherwise clinically euthyroid and previously stable TFT, leading to levothyroxine being withheld. This case report highlights the possibility of assay interference as a cause of discordant TFT. It also draws the importance of close collaboration between clinicians and the laboratory to avoid unnecessary investigations and inappropriate management of such a case.