A prospective study to assess the association of body mass index and contamination of urinalysis samples.

BACKGROUND: There is a commonly held belief that overweight women are more likely to offer contaminated urine samples (UAs) in the emergency department (ED) than women with normal body mass index (BMI). However, there is a paucity of research evaluating this potential concern. OBJECTIVE: We hypothesized that patients with higher BMI would be more likely to provide contaminated urine samples than women with low BMI. METHODS: This was a prospective, observational, cohort study evaluating consenting, adult, women that provided a clean catch, mid-stream sample at an inner-city ED. UAs were ordered at the discretion of the caring physician, cultures based on standardized parameters. The primary outcome parameter was the presence of UA contamination as defined by our microbiology lab. Demographic/historical data and BMI were recorded on a structured data sheet. Categorical data were analyzed by chi-square; continuous data by t-tests. Multivariable logistic regression was performed to control for confounding. RESULTS: There were 350 patients in the study group; 22% overweight, 35% obese, 17% morbidly obese, mean BMI 31. 5, and 60% provided contaminated specimens. The mean BMIs of the subjects with contaminated vs. uncontaminated UAs were significantly different (32.7 ±â€¯10.2 vs 29.7 ±â€¯8.8, p < 0.01). Within our multiple variable logistic regression model, obese and morbidly obese patients were more likely to provide contaminated UAs, while there were no significant associations for contamination with other variables except for hypertension (OR = 1.85, p = 0.02). CONCLUSION: Obesity was significantly associated with contamination of clean catch mid-stream samples in our population.