The Degree of Pyuria Can Help Determine Urinary Tract Infection in Elderly Women
By Richard R. Watkins, MD, MS, FACP, FIDSA, FISAC
Professor of Internal Medicine, Northeast Ohio Medical University, Rootstown, OH
SYNOPSIS: Elderly women with a urinary tract infection recorded a higher median number of urinary leukocytes compared to uninfected controls, including those with asymptomatic bacteriuria. For 264 leukocytes/µL, the sensitivity and specificity of microscopy were 88%. Using the standard pyuria threshold of 10 leukocytes/µL gave a specificity of 36% and a sensitivity of 100%.
SOURCE: Bilsen MP, Aantjes MJ, van Andel E, et al. Current pyuria cutoffs promote inappropriate urinary tract infection diagnosis in older women. Clin Infect Dis 2023;76:2070-2076.
Differentiating urinary tract infection (UTI) from asymptomatic bacteriuria (ASB) can be challenging in clinical practice. This is especially true in elderly patients, who may not manifest typical symptoms and cognitive impairment may have limited their communication abilities. Bilsen et al sought to determine whether the degree of urinary leukocytosis could help distinguish UTI from uninfected controls, including those with ASB.
The study was conducted in the Netherlands. The authors recruited subjects from hospitals, primary care centers, and senior living and long-term care facilities. Women age 65 years and older were included. Exclusion criteria were an inability to express symptoms, the presence of an indwelling urinary catheter, immunosuppressive use, antimicrobial use within 48 hours, current urolithiasis, and a UTI within the preceding month.
To be included in the UTI group, subjects had to have at least two new-onset lower UT symptoms (i.e., dysuria, frequency, urgency, or suprapubic pain); pyuria, defined as ≥ 10 leukocytes/µL or five or more leukocytes/high powered field or the presence of leukocyte esterase; and a monoculture (i.e., one uropathogen ≥ 104 colony forming units/mL). Researchers used fever, defined as a temperature 38° C or higher, to differentiate lower from upper UTI.
Community-dwelling women and long-term care residents who did not report any lower UT symptoms or fever were eligible to serve as controls. They were divided into three groups: ASB (defined as submitting at least two consecutive urine cultures [two to four weeks apart] with the same uropathogen with 105 CFU/mL or greater), negative culture, and mixed flora. Investigators considered Enterobacterales, enterococci, Pseudomonas aeruginosa, Staphylococcus saprophyticus, and group B streptococci as uropathogens.
There were 164 subjects included in the primary analysis, 63 in the UTI group and 101 controls. Their mean age was 78.3 years. The baseline characteristics between the UTI group and controls were well matched, although the control group contained more long-term care residents than the UTI group (43/101 vs. 7/63, respectively). Compared to controls, subjects with a UTI recorded a higher median level of urinary leukocytes (microscopy: 26 leukocytes/µL vs. 900 leukocytes/µL; flow cytometry: 23 leukocytes/µL vs. 1,575 leukocytes/µL; P < 0.001). The median leukocyte values were higher for subjects with UTI compared to those with ASB (microscopy: 900 leukocytes/µL vs. 296 leukocytes/µL [P = 0.002]; flow cytometry: 1,575 leukocytes/µL vs. 197 leukocytes/µL [P = 0.004]).
Using a cutoff of 264 leukocytes/µL, the sensitivity and specificity of microscopy were 88% (95% CI, 77%-94%; positive and negative likelihood ratio [LR]: 7.2 and 0.1, respectively). Flow cytometry demonstrated a sensitivity of 91% (95% CI, 79%-98%) and a specificity of 86% (95% CI, 78%-92%) using a cutoff value of 231 leukocytes/µL, with a positive LR of 6.5 and a negative LR of 0.1. Furthermore, the clinically used cutoff for UTI of 10 leukocytes/µL carried a sensitivity of 100% (95% CI, 94%-100%) with a specificity of only 36% (95% CI, 28%-48%). A cutoff of 100 cells raised specificity to 71% (95% CI, 61%-79%) and decreased sensitivity to 93% (95% CI, 84%-98%), while a cutoff of 400 cells increased specificity to 92% (95% CI, 86%-96%) and dropped sensitivity to 77% (95% CI, 65%-87%).
COMMENTARY
This was an interesting study that produced two main results. First, the degree of urinary leukocytosis can help distinguish UTI from noninfection in elderly women, including those with ASB. Second, the currently used definition of pyuria (10 leukocytes/µL) carries a low specificity for UTI in elderly women. Thus, clinicians need to reconsider the dogma that 10 leukocytes in a urinalysis equals a UTI in an elderly woman. In light of the findings, reassessing this threshold in other patient populations at higher risk for UTIs seems warranted. Multiple pyuria thresholds may need to be developed.
Like all studies, there were some limitations to this one to consider. First, because the study only included elderly women, the results should not be generalized to other types of patients. Second, the control group included more long-term care residents than the UTI group, which may have been a confounding variable that affected the results. Third, there may have been some UTI cases that were excluded because of the investigators’ uropathogen definition.
Nevertheless, this study provides good evidence suggesting the diagnostic threshold for pyuria in elderly women needs to increase. Indeed, 300 leukocytes/µL would be more reasonable, raising specificity (88%) to avoid overtreatment while still maintaining an adequate sensitivity (84%). Of course, pyuria levels should be interpreted in the clinical context of individual patients and should never be the only determining factor for making a UTI diagnosis.
Elderly women with a urinary tract infection recorded a higher median number of urinary leukocytes compared to uninfected controls, including those with asymptomatic bacteriuria. For 264 leukocytes/µL, the sensitivity and specificity of microscopy were 88%. Using the standard pyuria threshold of 10 leukocytes/µL gave a specificity of 36% and a sensitivity of 100%.
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