Urinary sIgA in children with urinary tract infection

Urinary secretory IgA (sIgA) was measured using a specific ELISA with insolubilized anti-IgA and enzyme-linked antisecretory component. This test was applied to unprocessed urine from healthy children and from children with urinary tract infection. Normal range was a function of age. In 175 healthy children the excretion rate of sIgA was low in infants younger than 6 months but was constant between ages 6 months to 15 years (median 0.69 mg/gm creatinine, range 0.15 to 3.4 mg/gm creatinine), whereas sIgA concentration (milligrams per liter of urine) increased continuously with age. No sex difference was noted. There were no significant circadian changes or day-to-day variability. Thirty girls, age 1 to 16 years, were examined; they had a history of recurrent symptomatic episodes of urinary tract infection but had anatomically normal tracts and no symptoms, and no bacteriuria at the time of study. sIgA excretion rate was significantly lower (0.45 mg/gm, creatinine, 0.08 to 0.75 mg/gm creatinine) than in controls. In contrast, 11 girls examined at the time of symptomatic urinary tract infections, and who had normal urinary tracts, had significantly (P less than 0.01) higher sIgA excretion rates (1.4 mg/gm creatinine, 0.8 to 3.4 mg/gm creatinine) than those in either control subjects or girls without symptoms at the time of study. Urinary sIgA excretion rates were highest (2.0 mg/gm creatinine, 0.44 to 3.69 mg/gm creatinine) in children with symptomatic urinary tract infections who had an abnormal urinary tract. We conclude that low urinary sIgA values may be a marker for recurrent symptomatic bacteriuria in girls with normal urinary tracts.