Increased body mass index among women correlates with increased rates of urine sample contamination [poster]
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Study Objectives: The diagnosis of urinary tract infection (UTI) depends on an accurate urinalysis (UA). An accurate UA requires a clean catch urine sample without contamination. Obtaining this can be a challenging task, particularly for obese women. We sought to determine the rates of urine contamination using various body mass index cutoffs. Methods: We retrospectively analyzed a seven month convenience sample of urine culture results (Jan-Jul 2012). Inclusion criteria were: diagnosis of UTI, female gender, clean catch sample, urine culture obtained and body mass index (BMI) information available. Patients were excluded if they were known to be pregnant. Two researchers independently evaluated each culture to determine if the culture was consistent with the diagnosis of UTI and to determine if the culture showed evidence of contamination. Results: A total of 7,134 urine cultures met the inclusion criteria and were analyzed. 26.4% of cultures were consistent with the diagnosis of UTI and 50.1% showed contamination. 30.4% of the positive cultures had contamination. Rates of positive culture were stable regardless of BMI. A BMI greater than 35 was associated with more frequent contamination (Odds Ratio 1.41) and higher rates of UA markers used for diagnosing UTI including nitrites, white blood cells and bacteria when compared with patients with a BMI less than 35. Conclusion: There are significantly higher rates of urine culture contamination and UA markers for UTI among obese women. Clinicians should consider this when assessing for or diagnosing UTI as overdiagnosis can lead to overtreatment including inappropriate use of antibiotics.