Sensitivity of the dipstick in detecting bacteremic urinary tract infections in elderly hospitalized patients

Abstract

Background: The sensitivity of the dipstick in elderly patients with a suspected urinary tract infection (UTI) is unclear because of the inclusion of patients with urine contamination or asymptomatic bacteriuria in previous studies. Methods: We selected consecutive patients aged 65 years or older hospitalized in internal medicine departments with bacteremic UTI (same organism in blood and urine cultures) minimizing misclassifications. The false positive rate was determined in consecutive patients with negative culture results. A positive dipstick was a test result with a trace leukocyte esterase and/ or nitrite positivity. Bacteriuria was the growth of at least 105 colony-forming units per milliliter of urine. Results: Of 20,555 consecutive patients, 228 had a bacteremic UTI, and 4069 a negative culture result. The sensitivity of the dipstick was 96.9% (95% CI—93.7–98.6) with a false positive rate of 42.4% (95% CI, 41.0–43.8) in those with a negative culture result. Conclusions: In elderly hospitalized patients with a bacteremic UTI, the dipstick urinalysis is highly sensitive, much higher than reported previously in studies of UTIs in the elderly. It is unclear whether the observed high sensitivity of the dipstick was due to the exclusion of patients with asymptomatic bacteriuria or to spectrum bias. Studies of the clinical utility/disutility of using a negative dipstick to rule out a urinary tract infection are warranted.