Abnormal function of renal tubules in patients with simple renal cysts.

The present study aimed to assess the function of proximal and distal tubules in patients with simple renal cysts. Thirty-one patients with simple renal cysts and 10 healthy subjects were examined. Based on the cyst fluid/plasma sodium ratio, 25 cysts were found to be of proximal origin and 6 of undetermined origin. In all patients cyst fluid and plasma concentrations of beta-2-microglobulin (beta-2-MG), sodium, potassium, calcium, phosphorus and total protein were assessed. Urinary excretions of sodium, potassium, calcium, phosphorus, beta-2-MG and Tamm-Horsfall protein (THP) were also estimated. Fractional excretion of beta-2-MG was calculated. The concentrations of beta-2-MG in fluid obtained from cysts of proximal origin were significantly higher than in fluid from cysts of undetermined origin (2.26 +/- 0 36 vs. 0.65 +/- 0.13 mg/l, p = 0.0004). Concentrations of THP (6.85 +/- 1.21 vs. 3.14 +/- 1.06 micrograms/ml, p < 0.05), and potassium (4.39 +/- 0.07 vs. 3.13 +/- 0.44 mmol/l, p < 0.05) were also higher in fluid from proximal cysts than in fluid from cysts of undetermined origin. Plasma beta-2-MG concentration was significantly higher in patients with proximal and undetermined cysts than in the control group (4.35 +/- 0.34 and 4.11 +/- 0.74 vs. 1.89 +/- 0.1 mg/l, p < 0.001). Urinary beta-2-MG excretion was also significantly higher in both groups of patients than in healthy subjects (474.8 +/- 165.9 and 346 +/- 94 vs. 100.2 +/- 19.6 micrograms/24 h, p < 0.05). Urinary THP excretion was significantly higher in patients with proximal cysts than in healthy subjects (31.0 +/- 5.1 vs. 16.3 +/- 2.5 mg/24 h, p < 0.05). From the results obtained in this study it seems that patients with simple renal cysts of proximal origin are characterized by abnormal tubular handling of beta-2-MG, and calcium and THP excretion. Thus, in patients with proximal cysts presence of a latent renal tubulopathy seems to be likely.