Effects of Levothyroxine Treatment on Hemodynamic and Isotopic Renal Functions in Subclinical Hypothyroidism

Animal experimental hypothyroidism is associated with renal and hemodynamic abnormalities. In human, exact measurements of GFR showed a decline in GFR after thyroidectomy and an increase in GFR and renal blood flow after hormone replacement. Renal and cardiovascular effects of subclinical hypothyroidism, defined by a high TSH and normal T4 are less known and the indications for treatment of subclinical hypothyroidism are subject to controversies. A retrospective study suggests that treatment of subclinical hypothyroidism may slow the degradation rate of renal function estimated by MDRD. However, the potential hemodynamic benefit of treatment has not yet been studied.

The investigators propose to assess whether the hormone replacement for subclinical hypothyroidism in patients with chronic kidney disease is beneficial for hemodynamic and renal functions and which mechanisms are involved.

Isotopic measurements of glomerular filtration and renal blood flow and an hemodynamic evaluation by transthoracic echocardiography and flow-mediated vasodilation will be carried out before and 6 months after substitution. This open prospective study will include 16 patients in order to detect an increase of 1.2 standard deviation for the measured glomerular filtration.