RESUMO
The existing classifications of simple renal cysts are based on cyst fluid sodium concentration or cyst fluid/plasma sodium ratio. The present study aimed to assess: 1) the usefulness of cyst fluid concentrations of beta-2-microglobulin (beta-2-MG) as a marker of proximal tubules function and Tamm-Horsfall protein (THP) as a marker of distal tubules function to define the origin of renal cysts (proximal or distal); and 2) the function of proximal and distal tubules in patients with simple renal cysts. 31 patients with simple renal cysts and 10 healthy subjects were examined. Basing on the cyst fluid/plasma sodium ratio, 25 cysts were classified as of proximal origin and 6 as of undetermined origin. In all patients cyst fluid and plasma concentrations of beta-2-MG, erythropoietin, sodium, potassium and total protein were assessed. Urinary excretion of beta-2-MG and THP was also estimated and fractional excretion of beta-2-MG was calculated. The concentration 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), erythropoietin (500.6 +/- 176.8 vs. 42.0 +/- 17.7 mU/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.(ABSTRACT TRUNCATED AT 250 WORDS)