Hyperthyroxinemia and clinical euthyroidism. Report of one case

The association of hyperthyroxinemia and euthyroidism is frequent and chara cterized by high plasma thyroxin concentrations, normal TSH values and abse nce of clinical signs of hyperthyroidism. We report an asymptomatic 28 year s old male presenting with a serum total plasma thyroxin of 18.5 mu g.gl (N 6.1-12.5), a free thyroxin of 2.9 ng/dl (N 0.8-1.4) a TSH of 3.4 mu IU/ml (N 0.5-5), and a triiodothyronine of 128 ng/dl (N 80-180). Laboratory asses sment did not find high thyroxin binding globulin, albumin or prealbumin co ncentrations or antithyroxin antibodies. The thyroxin binding capacity of a lbumin was elevated to 58.2 mu g/dl (N 11.5-34.1). TSH responded normally t o TRH stimulus and was suppressed with exogenous triiodothyronine, which ca used an hyperthyroid syndrome. We concluded that this patient had a familia l dysalbuminemia.