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Bacteria on urine microscopy is not associated with systemic infection in patients with obstructing urolithiasis
Felix Cheung, MD, Charles A. Loeb, BA, Michael P. Croglio, BS, Wayne C. Waltzer, MD, Steven J. Weissbart, MD.
Stony Brook University Hospital, Stony Brook, NY, USA.
BACKGROUND: Bacteria are commonly found on urine microscopy in emergency room (ER) patients with obstructing urolithiasis. However, the clinical significance of this finding is unclear. Determining whether or not bacterial presence on urine microscopy represents infection is important as ureteral stent placement is indicated in patients with obstructing urolithiasis and infection. We aim to investigate if the presence of bacteria on urine microscopy is associated with other markers of infection in patients with obstructing urolithiasis presenting to the ER.
METHODS: We performed a cross sectional study of 199 patients presenting to the ER with obstructing urolithiasis and divided patients into two groups according to the presence of bacteria on urine microscopy. The primary outcome was serum white blood cell count (WBC >10,800/hpf) and secondary outcomes were objective fever, subjective fever, tachycardia (>100 bpm), pyuria, and final urine culture. Univariate and multivariate analysis were used to assess if the presence of bacteria on microscopy was associated with other markers of infection.
RESULTS: The study included 72 patients in the bacteriuria group and 127 without bacteriuria. On univariate analysis, the presence of bacteria was not associated with leukocytosis, objective fever, or subjective fever (table 1), but was associated with gender (P<0.001), pyuria (P<0.001), positive nitrites (P=0.001), positive leukocyte esterase (P<0.001), and squamous epithelial cells (P=0.002). In a multilinear regression model including the presence of squamous cells, age, and sex, the presence of bacteriuria was not related to serum white blood cell count (coefficient -0.47; 95% CI -1.1 - 0.2; P=0.17), heart rate (coefficient 0.85; 95% CI -2.5 - 4.2; P=0.62), presence of subjective or objective fever (OR 1.5; 95% CI 0.8 - 3.1; P=0.18), or the presence of squamous epithelial cells (coefficient -4.4; 95% CI -10 - 1.2; P=0.12). However, the presence of bacteriuria was related to only the degree of pyuria (coefficient 16.4; 95% CI 9.6 - 23.3; P<0.001).
CONCLUSIONS: Bacteria on urine microscopy was not associated with other markers of systemic infection and may largely represent a contaminant. Renal colic may be a risk factor for providing a contaminated urine specimen.
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