Can urine cultures and reagent test strips be used to diagnose urinary tract infection in elderly emergency department patients without focal urinary symptoms?

OBJECTIVE To compare the results of urine cultures and reagent strip testing in 2 groups of elderly emergency department (ED) patients: an asymptomatic group unlikely to have urinary tract infection (UTI), and a group who had vague symptoms and were considered at risk for UTI. METHODS We performed a prospective observational convenience study with 2 groups of 100 patients aged 65 or older. The asymptomatic group consisted of afebrile patients presenting to the ED with non-infectious complaints, while the symptomatic group included patients presenting with acute confusion, weakness or fever but no apparent urinary symptoms. We defined a positive urine culture as a single organism count greater than 100,000 CFU/mL in mid-stream specimens, or greater than 1000 CFU/mL in catheter specimens. We considered reagent strips positive if they demonstrated any reaction to the leukocyte-esterase assay, the nitrite assay or both. RESULTS Of the 33 positive cultures, 10 had negative reagent strips. Thirteen of the 14 positive nitrite tests were culture positive for a specificity of 92.8% and a sensitivity of 36.1%. Positive cultures did not infer a diagnosis of UTI. Of the 67 positive reagent strips, 41 (61.2%) were associated with negative cultures. Likelihood ratios (LRs) in both groups affirmed the inability of the reagent strips to help significantly in decision making, with positive and negative LR in the indeterminate range (control group: 2.8 and 0.31, symptomatic group: 2.7 and 0.46, respectively). CONCLUSION In the elderly, reagent testing is an unreliable method of identifying patients with positive urine [corrected] cultures. Moreover, positive urine culture rates are only slightly higher in patients with vague symptoms attributable to UTI than they are in (asymptomatic) patients treated for non-urologic problems, which suggests that many positive cultures in elderly patients with non- focal systemic symptoms are false-positive tests reflecting asymptomatic bacteriuria and not UTIs. Blood cultures, regarded by many as the criterion standard for UTI, do not have sufficient specificity to confirm the diagnosis of UTI in elderly patients with non-specific symptoms.