Endocrine Abstracts

An 88 year-old male was referred to Endocrine Clinic with abnormal thyroid function test (TFT); free T4:fT4: 36.9pmol/L (NR:11-23) and a normal TSH:2.51mU/L (NR:0.35-5). Atrial Fibrilation was diagnosed recently and was on Apixiban and Bisoprolol. He had history of prostate cancer, hypertension, oesophagitis, cervical spondylosis, splenectomy and CKD3. He felt well apart from slight heartburn. He was a retired motor engineer. He had no family history of thyroid disease and never had TFT checked in the past. Examination was normal. he was followed up in clinic regularly and free T4 was found to be persistently raised (fT4 from 55 to 59pmol/L with normal TSH from December 2017 till March 2018) on 4 occasions. He remained clinically euthyroid and was not commenced on treatment. Thyroid antibodies were negative. Other blood tests, and pituitary/brain MRI were normal. Thyroid hormone assay interference was suspected; His TFTs were repeated at a different laboratory, Wythenshawe Hospital in Manchester which revealed normal TFT (f T4 12.0, f T3 3.1, TSH 1.90). Family was screened for the possibility of thyroid hormone resistance; two daughters were found to have normal TFT. Raised fT4 from blood tests carried out at Royal Preston Hospital was a result of assay interference and the patient was discharged from the clinic. This case report highlights that Thyroid hormone assay interference should be considered where TFTs do not fit the clinical picture or are incongruent to each other. Occasionally, TFTs can be difficult to interpret; careful reassessment of thyroid status is required. Failure to reach the correct diagnosis may result in inappropriate management. Following reassessment of possible confounding factors, if TFTs remain discordant, consider assay interference as a possible cause. After this, consider screening for genetic disorders of the hypothalamic-pituitary-thyroid axis – rare causes of anomalous TFTs.