What is the optimal leukocyte cutoff for diagnosing urinary tract infection in older women?
For women 65 years and older, we should use a much higher cutoff for pyuria before diagnosing UTI to avoid overtreating women who have asymptomatic bacteriuria. A limitation of this diagnostic case-control design is that it tends to overestimate the accuracy of a test, so a follow-up study using a cohort design and women with clinically suspected UTI should be done next. (LOE = 4)
Overuse alert: This POEM aligns with the Canadian Nurses Association’s Choosing Wisely Canada recommendation: Don’t recommend antimicrobials to treat bacteriuria in older adults unless specific urinary tract symptoms are present. A patient handout is also available on reducing unnecessary antibiotic use.
Diagnostic test evaluation
The usual cutoffs for diagnosing urinary tract infection (UTI) are greater than 10 leukocytes/microliter (mcl) or greater than 5 to 10 leukocytes/high-powered field. However, these cutoffs were derived from studies of premenopausal women. Approximately 20% of older women have asymptomatic bacteriuria (ASB), and 90% of them also have some degree of pyuria. To identify the optimal leukocyte cutoff for a diagnosis of UTI in older women, these researchers identified 63 women, 65 years and older, with UTI based on a positive urine culture for a uropathogen, at least 2 lower urinary tract symptoms (LUTS), and at least 10 leukocytes/mcl. The comparison group consisted of 101 community-dwelling women, 65 years or older, without LUTS; 18 had ASB, 25 had a negative urine culture, and 58 had a culture with mixed flora. All urine samples underwent automated microscopy and urine flow cytometry. The area under the curve for leukocytes as a test for UTI was 0.93 for both methods. The optimal cutoff for automated microscopy was greater than 265 leukocytes/mcl, which was 88% sensitive and 88% specific (positive likelihood ratio [LR+] 7.2; negative likelihood ratio [LR-] 0.14). For flow cytometry, the optimal cutoff was greater than 231 leukocytes/mcl, which was 91% sensitive and 86% specific (LR+ 6.5; LR- 0.10). And what about the cutoff of greater than 10 leukocytes/mcl? It was 100% sensitive, but only 36% specific.
Mark H. Ebell, MD, MS
University of Georgia