Excretion of Tamm-Horsfall protein in patients with uric acid stones

The cause of reduced Tamm-Horsfall protein excretion in patients suffering from uric acid diathesis is still unknown. Our investigation was conducted based on the hypothesis that the solubility of uric acid is increased by Tamm-Horsfall protein and that an increased uric acid content in the urine might cause a decrease in Tamm-Horsfall protein. In 20 patients with uric calculi the excretion of Tamm-Horsfall protein, uric acid, calcium, and citrate was measured. 65% of the patients had pure uric acid stones (group I) and 35% showed mixed stones with at least 30% of uric acid (group II). Reduced Tamm-Horsfall protein excretion was found in 63% of the patients of group I and in 43% of the patients of group II. The excretion of Tamm-Horsfall protein was significantly reduced in pure uric acid stone formers compared to normal subjects (p < 0.0001). The excretion of uric acid was elevated in 61% of the patients of group I and in 86% of the patients of group II. There was no significant correlation between Tamm-Horsfall protein excretion and uric acid excretion (r = 0.2139). Calcium excretion was elevated in 57% of the patients with mixed stones. The excretion of citrate was reduced in almost all of the patients of groups I and II. Ou results do not support the hypothesis that an increased content of uric acid in the urine causes a decrease in Tamm-Horsfall protein. In our opinion the lower excretion of Tamm-Horsfall protein in some of the stone patients might be caused by damage in the distal tubular epithelium. Moreover, it has to be supposed that there are defects both in the distal and the proximal tubule in patients prone to develop uric acid calculi.