A revalidation and critique of assumptions about urinary sample collection methods, specimen quality and contamination

Linda Collins,Jennifer Rohn,Sanchutha Sathiananthamoorthy,James Malone-Lee

doi:10.1007/s00192-020-04272-x

Abstract

Introduction and hypothesisMidstream urine (MSU) is key in assessing lower urinary tract syndrome (LUTS), but contingent on some assumptions. The aim of this study was to compare the occurrence of contamination and the quality of substrates obtained from four different collections: MSU, catheter specimen urine (CSU), a commercial MSU collecting device (Peezy) and a natural void. Contamination was quantified by differential, uroplakin-positive, urothelial cell counts.MethodsThis was a single blind, crossover study conducted in two phases. First, we compared the MSU with CSU using urine culture, pyuria counts and differential counting of epithelial cells after immunofluorescence staining for uroplakin III (UP3). Second, we compared the three non-invasive (MSU, Peezy MSU™, natural void) methods using UP3 antibody staining only.ResultsThe natural void was best at collecting bladder urinary sediment, with the majority of epithelial cells present derived from the urinary tract. CSU sampling missed much of the urinary sediment and showed sparse culture results. Finally, the MSU collection methods did not capture much of the bladder sediment.ConclusionWe found little evidence for contamination with the four methods. Natural void was the best method for harvesting shed urothelial cells and white blood cells. It provides a richer sample of the inflammatory exudate, including parasitised urothelial cells and the microbial substrate. However, if the midstream sample is believed to be important, the MSU collection device is advantageous.

Highlights

Introduction and hypothesisMidstream urine (MSU) is key in assessing lower urinary tract syndrome (LUTS), but contingent on some assumptions
A urinary tract infection (UTI) is a debilitating condition causing the onset of painful urination, increased urinary frequency, the inability to start urinating and the sensation of a sudden need to urinate [5], all of which are classified as lower urinary tract symptoms (LUTS) [6]
The literature shows that the methods of sample collection for urine culture have never been validated in appropriate clinical trials

Summary

Introduction

Midstream urine (MSU) is key in assessing lower urinary tract syndrome (LUTS), but contingent on some assumptions. Dipstick analyses are surrogate tests, referenced not to microscopic pyuria but to a gold standard urine culture threshold for UTI, which guidelines accept as being between 103 cfu ml−1 and 106 cfu ml−1 of the pure growth of a single urinary pathogen [8]. This test has attracted criticism too [9,10,11]. It is recognised that routine urinalyses, including dipstick and culture, are insensitive, missing genuine infection in many symptomatic patients [12,13,14]

Objectives

Methods

Results