Endocrine Abstracts

Introduction: Discordant thyroid function tests are frequently identified in clinical practice and should raise suspicions about laboratory analytical interference.

Case report: A 59 year old male was referred to Endocrine services for abnormal thyroid function tests following his recent Emergency department presentation with palpitations. His TFT (Roche) showed FT4 level was raised at 27.1 pmol/l (6.5 - 17.0), and his TSH normal at 2.57 uIU/ml (0.34 - 5.60) indicating a discordant TFT pattern. Clinically he was euthyroid. An incidental discovery of possible left-sided pituitary microadenoma was reported during a previous MRI brain scan done for TIA. Subsequently MRI scan of the pituitary was performed and reported an area of signal intensity that was not typical for a microadenoma. In view of discordant TFT results, further serum samples were sent to external laboratory (Delfia) to rule out assay interference. With the results of TSH 2.42 mU/l (0.40-4.00), FT4 17.6 pmol/l (9.0-20.0), total T4 216.8 nmol/l (69.0-141.0), TBG 26.2 ug/ml (14.0-31.0), it was confirmed that discordant pattern of thyroid function could be due to assay interference. Subsequently genetic testing was undertaken which confirmed Familial dysalbuminaemic hyperthyroxinaemia (FDH) in which a mutant (R218H), circulating albumin protein caused falsely elevated thyroid hormone (FT4, FT3) results in some measurement methods.

Conclusions: Familial dysalbuminaemic hyperthyroxinaemia is an inherited condition caused by mutations in the ALB gene, which encodes circulating albumin protein (Larsen et al., 2008). FDH may be more frequent than previously thought, despite the fact that its prevalence is unknown. The mutant albumin has an increased affinity for T4 resulting in discordant thyroid function tests (TFTs). The biochemical profile demonstrates increased serum T4 concentrations with normal FT4, total serum T3, and TSH levels. Biochemical tests and albumin genotyping can be used as a means to confirm the diagnosis of FDH. Because all of the mutations linked to FDH so far have involved residue in the albumin molecule, molecular genetic testing is rather easy and yields a clear result (Cartwright et al., 2009).