Familial dysalbuminaemic hyperthyroxinaemia and other causes of euthyroid hyperthyroxinaemia

Clinical and biochemical studies on a family in which 3 members have familial dysalbuminaemic hyperthyroxinaemia (FDH) are presented. They were clinically euthyroid with elevated serum thyroxine (T4) and free T4 indices but normal free T4 by equilibrium dialysis and normal serum triiodothyronine (total and free). All thyroid function tests on the remaining family members were normal. The inheritance is consistent with autosomal dominance. Also presented are data on 4 unrelated patients with FDH and two patients with T4 autoantibodies. The methods for detecting FDH, T4 antibodies and other causes of euthyroid hyperthyroxinaemia are now freely available. Since these anomalies may be more common than previously supposed, clinical awareness of the conditions is necessary to protect patients from the consequences of incorrect diagnosis of thyrotoxicosis.