Bacteria-specific antibody in the urine of patients with acute pyelonephritis and cystitis

Urine specimens from 65 adult patients with symptomatic urinary tract infections that involved 91 episodes of well-defined acute pyelonephritis or cystitis were tested for antibody-coated bacteria (ACB) by a fluorescent antibody assay, unbound bacteria-specific antibody by radioimmunoassay (RIA), and levels of total protein and IgG. Acute pyelonephritis was associated with positive tests for ACB (22 [69%] of 32), elevated levels of unbound antibody (28 [88%] of 32), and a mean RIA binding ratio of 9.4. Cystitis was associated with negative tests for ACB (56 [95%] of 59), low levels of antibody in urine (38 [64%] of 59), and a mean RIA binding ratio of 3.2. The results showed that a negative test for ACB may occur with elevated levels of unbound antibody in the urine because, although elevated, levels were still too low to result in detectable antibody coating of the bacteria. There was often, but not always, a correlation between RIA binding ratios and levels of urinary protein and IgG.