Prevalence of familial dysalbuminemic hyperthyroxinemia in serum samples received for thyroid testing.

The prevalence of familial dysalbuminemic hyperthyroxinemia (FDH), a condition sometimes mistaken for hyperthyroidism, has not been clearly established. I present a study of the prevalence of FDH in serum samples received for thyroid-function tests in a reference laboratory. A prospective study of 15,674 serum samples was carried out over 24 months, of which 13,232 cases were from women (84.42%) and 2442 were from men (15.58%). FDH was diagnosed in 26 cases, 22 in women and four in men. Therefore, the prevalence of FDH in the total number of samples from both sexes was 0.17%, 0.17% in women, and 0.16% in men, which is consistent with a dominant autosomal type of familial transmission. These findings demonstrate that cases of FDH occur frequently; therefore, every laboratory must be prepared to recognize them and thus avoid an incorrect diagnosis of the patient's thyroid function.