The Association Between Clean Catch and Catheterized Urine Among Obese Patients

Objectives: Up to 42% of cultures collected through midstream clean catch result in contamination or growth of nonpathogenic flora which leads to overprescribing antibiotics. While there is guidance for urine sampling techniques for normal weight female populations, ambiguity exists for obese patients. We aimed to describe the associations between midstream clean catch and catheter specimens for obese female patients with a BMI >/= 30.

Methods: : Patients who presented to an academic urology department for evaluation with a BMI >/= 30 were recruited. Our primary outcome was to perform a paired analysis comparing each patient’s midstream clean catch urinalysis (UA) and urine culture to their catheter specimen. Midstream clean catch was collected first, and then the patients were catheterized. Both specimens were dipstick tested and sent for culture. The data were analyzed utilizing contingency tables comparing patient’s midstream UA to their catheterization sample within a single subject. Cohen’s Kappa statistic measured agreement between sample collection types.

Results: Of the 201 patients consented and agreed to be in the study, the average age was 59.6 +/- 13.4 years and BMI was 37.2 +/- 5.9 kg/m2. Dipstick hematuria readings were 67% congruent (k=0.45); nitrites were 97% congruent (k =0.65); leukocytes were 61% congruent (k=0.19); and bacteria were 54% (k=0.35). (Table) Midstream specimen collection values were higher for all but blood on dipstick testing. Bacteria culture specimen collection route were 36.9% congruent (k=0.23). Agreement for positive cultures requiring treatment was 10% (k= 0.23). Interestingly, 74.1% of the midstream urine culture samples reported mixed >3 bacteria vs none in the catheterized specimens (p < 0.001).

Conclusions: Among obese females, urine sample testing varied widely between collection method with poor agreement in results. Except for blood, midstream urine collection was more likely to grow pathogenic bacteria, and had a higher likelihood of indicating infection.