Endocrine Abstracts

Familial Dysalbuminaemic Hyperthyroxinaemia (FDH) is characterised by mutant albumin with increased affinity for thyroxine, and to a lesser extent triiodothyronine, giving falsely elevated fT4 and fT3 levels in standard assays. This may lead to inappropriate management of euthyroid patients, and complicate diagnosis and management of thyroid disease in patients with coexistent FDH. We report a case of Graves’ thyrotoxicosis complicated by underlying FDH. A 41-year-old woman presented with a history of symptomatic hyperthyroidism. Clinical examination showed tremor, tachycardia, diffuse goitre, and signs of thyroid eye disease. Biochemistry confirmed hyperthyroidism (TSH < 0.01, free T4 80.9, free T3 30.8) due to Graves thyrotoxicosis (TRAb antibody level 22.2). Neck Ultrasound showed a diffusely enlarged heterogenous and hypervascular thyroid gland. The patient underwent total thyroidectomy as definitive treatment after initial biochemical control was achieved with thionamide treatment. Thyroid function on replacement dose Levothyroxine 125 mg daily, showed discrepant results with a high T4(26.6 pmol/l) with non-suppressed TSH(0.72 mU/l). Assay interference was excluded. FDH was suspected and genetic analysis a showed heterozygosity for the c.725G>A p (Arg 242 His) pathogenic variant in the ALB gene, confirming FDH. While FDH may have contributed to the magnitude of elevation of the initial T4 and T3 on presentation, the diagnosis of Graves’ disease was secure given symptomatic hyperthyroidism, suppressed TSH, elevated TRAb and clinical symptoms and signs of thyroid eye disease. This case highlights difficulties in assessing thyroid status in patients with autoimmune thyroid disease and coexisting FDH, which may potentially result in inappropriate therapy. A high index of suspicion of underlying FDH as a cause for discordant thyroid function tests remains the cornerstone of diagnosis with TSH levels being the most reliable biochemical marker of thyroid status in patients with coexistent autoimmune thyroid disease.