Diagnostic value and biological significance of antibody-coated bacteria in urine.

The incidence of antibody-coated bacteria (ACB) in the urinary sediments as an indication of the site of urinary tract infections (UTI) was investigated in 103 adult subjects with persistent bacteriuria by means of a direct immunofluorescence technique.ACB were found in 49 of 58 (84.5%) subjects with long-standing upper urinary tract obstruction and in 5 of 45 (11.1%) with lower UTI; this difference was statistically significant (X(2) = 51.79; P<0.001). The group with upper UTI was further subdivided according to renal function (patients with renal insufficiency had both bilateral obstruction and bilateral renal damage); 21 positive results were obtained in 27 (77.8%) patients with normal renal function, whereas 28 positive cases were observed among 31 (90.3%) patients with chronic renal insufficiency. Thus the degree of renal involvement also seemed to influence the outcome of the test. Within the group of lower UTI, a higher rate of ;false-positive' results was obtained in 14 patients with symptomatic long-standing infection (21.4%) than in 31 subjects with asymptomatic bacteriuria (6.4%). The three major immunoglobulin classes and the secretory component were studied in 42 cases. Of these, 29 were found to be positive for ACB. The constant presence of IgA and secretory component on the surface of ACB suggests that the secretory immune system plays an important role in UTI.