Renal function directly related to thyroid function

The kidney is an important target of thyroid hormone action and its function is directly related to thyroid hormone levels, a study in The Netherlands has found.The study assessed 37 consecutive patients with previously untreated primary hypothyroidism caused by autoimmune thyroiditis, and 14 with untreated hyperthyroidism due to Graves' disease. Renal function was measured at baseline and at least three months after becoming euthyroid. Investigations included plasma creatinine and glomerular filtration as calculated from the Modification of Diet in Renal Disease (MDRD) formula.In patients with hypothyroidism, mean plasma creatinine decreased and mean estimated GFR increased after treatment. Twelve of the 37 patients had elevated creatinine (more than 90 micromol/l) at baseline, and four remained slightly elevated despite thyroid replacement therapy. They also had TSH levels within the subclinical hypothyroid range despite normal free T4 levels and no clinical symptoms of hypothyroidism.In the patients with hyperthyroidism, plasma creatinine increased and estimated GFR declined after treatment. Three of the 17 patients had creatinine levels lower than 40 micromol/l at baseline, and three had levels just above 90 micromol/l after treatment. There was a clear correlation between changes in thyroid function and changes in renal function in both groups. "The kidney, in addition to the brain, heart and muscle, is an important target of the action of thyroid hormones," the study concluded. Possible explanations for the link included an effect of thyroid hormone on circulating volume, cardiac function and therefore renal blood flow, and changes in muscle mass and muscle production of creatinine.Changes in parameters of renal function were often subtle and remained within the normal range, making the link difficult to discern in routine practice. However, the "set point" of thyroid function for each individual tended to be quite rigid, and small changes could have considerable significance despite remaining within normal limits for the population as a whole.Reference...