Performance measure of urinary antigen in patients with Streptococcus pneumoniae bacteremia

The Streptococcus pneumoniae (SP) urinary antigen (UAg) test is a commonly used assay. The purpose of this study was to evaluate the test's actual performance in the clinical setting and determine the effects of renal function, grade of bacteremia, and severity-of-illness scores on its outcome. Patients with pneumococcal bacteremia were retrospectively identified and stratified on the basis of glomerular filtration rates, number of positive blood cultures, and CURB-65 scores. Logistic regression was used to determine the effect that these 3 variables had on test outcomes. SP UAg testing was performed in 65 of 129 patients with pneumococcal bacteremia and was positive in 42 of 65 (64.5%). Impaired renal function was the only variable to have a significant effect on test outcome (P = 0.03). Test performance was less sensitive than prospective studies indicate. Patients with impaired renal function were significantly more likely to have positive UAg tests.