Urinary infection may invalidate the double-sugar test of intestinal permeability.

To assess the effect of urinary infection on a typical double-sugar test of intestinal permeability, rhamnose and cellobiose were added to 12 infected urine samples to give sugar concentrations generally present in the 5-h urine samples of patients undergoing the test. Rhamnose concentration fell by approximately 20% in two of the specimens after incubation at 37 degrees C for 5 h. Eight of the 12 samples showed a fall in cellobiose concentration at 2.5 h, and 11 at 5 h. On five occasions more than 90% of the cellobiose was destroyed within 5 h. Yet only eight of these urine samples contained organisms that were able to metabolize cellobiose. This apparent anomaly may have resulted from bacteria surviving in spite of the thiomersal preservative, and then consuming the glucose to which the cellobiose was hydrolysed to enable calculation of cellobiose concentration. We conclude that bacteriuria may invalidate the result of the double-sugar test of intestinal function.