Alteration of renal function in hyperthyroidism: increased tubular secretion of creatinine and decreased distal tubule delivery of chloride.

In 77 untreated patients (16 males and 61 females, aged 12 to 65 years) with hyperthyroid Graves' disease, and in 107 control subjects (36 males and 71 females, aged 13 to 78 years), blood urea nitrogen (BUN), serum creatinine (Scr) levels, and BUN to Scr ratios (BUN/Scr) were determined. In 53 patients, the determinations were performed before treatment and after restoration of euthyroidism by treatment with an antithyroid drug. In addition, in seven untreated patients and seven normal subjects, renal clearances of creatinine (Ccr), urea nitrogen (Cun), inulin (Cin), and p-aminohippurate (CPAH) were also determined. The distal tubule delivery of chloride (DTD) and the distal fractional chloride reabsorption (DFCR) were also measured in these subjects: DTD = (CH2O + Ccl)/Cin x 100, and DFCR = CH20/(H20 + Ccl) x 100, where CH20 and Ccl stand for clearances of H2O and chloride, respectively. BUN was significantly elevated, while Scr was significantly depressed, in untreated patients with hyperthyroid Graves' disease. Accordingly, the BUN/Scr was markedly elevated. Restoration of euthyroidism accompanied the normalization of all these abnormalities. Ccr and Cun were significantly elevated, but Cin (glomerular filtration rate [GFR]) was slightly, but insignificantly, elevated in the patients. As a result, the ratios Ccr/Cin and Cun/Cin were significantly greater in the patients than in controls (Ccr/Cin, 1.42 v 1.00; Cun/Cin, 0.92 v 0.68). The amounts of urinary creatinine and urea nitrogen (UN) excretion were decreased and increased, respectively, and DTD was significantly depressed, but DFCR was unchanged in the patients. We conclude that BUN is elevated, Scr is depressed, and the BUN/Scr is increased in hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)