Blood volumes and renal function in overt and subclinical primary hypothyroidism

Introduction: Thyroid dysfunction is associated with marked alterations in cardiovascular and renal functions. In hypothyroidism, myocardial contracti lity, cardiac output, and oxygen consumption are decreased, whereas periphe ral resistance is increased. Methods: We assessed blood volumes and effecti ve renal plasma blood flow (ERPF) and glomerular filtration rate (GFR) in 1 7 patients with overt primary hypothyroidism and in 15 of these patients wh en in euthyroid state after substitutive therapy. We performed the same mea surements in eight patients with subclinical hypothyroidism. Results: In th e hypothyroid state, the plasma volume measured by dilution of I-125-albumi n (APV) was higher than the calculated plasma volume (CPV) from packed red cell mass, suggesting an extravascular escape of albumin. After substitutiv e therapy, the CPV showed a statistical increase (P < 0.05), whereas APV re mained unchanged. Both ERPF and GFR increased after thyroxine therapy (p < 0.05). In the subclinical group, blood volumes and renal function were simi lar to those found in the other group of patients when in the euthyroid sta te. Conclusions: We conclude that in primary hypothyroidism, ERPF and GFR a re low, but that these values improve with substitutive therapy. CPV is a b etter index of the current plasma volume than APV. The difference between t hese two parameters suggests that the escape of albumin into the extravascu lar space in primary hypothyroidism is terminated by treatment. There are n o clear abnormalities either in blood volumes or in renal function in subcl inical hypothyroidism.