Specimen collection technique and standards for diagnosing urinary tract infections

Abstract

A urinary tract infection (UTI) is one of the leading reasons for treatment in primary healthcare. It is estimated that 50% of the female population in the UK will have least one occurrence of the infection in their lifetime. It is a debilitating condition and causes a variety of lower urinary tract symptoms (LUTS). The recommended practice for detecting a UTI is by analysing a urine specimen and culturing the sample for bacterial growth and antibiotic sensitivities. There are two main specimen collection methods: the midstream urine (MSU) and the catheter specimen of urine (CSU). The CSU is recognised as the gold standard, but requires an invasive procedure. The MSU which is the non-invasive clinical standard is regarded as insufficient because the method is frequently reported as contaminated with skin and vaginal flora, but the definitions of contamination in the literature varies. Drawing on the published body of knowledge, this study aimed to investigate and determine what constitutes contamination using microbiological culturing and the uroplakin-3 cell staining technique that detects the presence of cells that originate from the bladder.

A two phase, single blind, cross over design study was conducted, comparing four different urine specimen collection methods. Experiment one tested the hypothesis that a MSU has equal merits to a CSU when capturing urothelial cells that are indicative of a UTI. A total of 60 patients and 30 controls were recruited into the study. The MSU specimens were compared with the CSU specimens to determine urinary cell origin using uroplakin-3 staining. The findings proved that the cells found in the MSU were not contaminants as commonly assumed, but were inflammatory markers of infection invading the lower urinary tract. Experiment two tested the hypothesis that if a MSU has equal merits to a CSU, then a directly voided urine specimen (natural urination) will be the optimal method when capturing the majority of urothelial cells that have been exfoliated from the bladder. A total of 31 patients were recruited and the MSU specimens were compared with the directly voided urine to determine the proportion of cells that originate from the bladder. The findings demonstrated that the directly voided urine was the optimal method and had the ability to capture predominant urothelial cells.

A qualitative study of patient views and experiences of urine specimen collection was conducted. Thirty patients were interviewed and the data were analysed for recurrent themes. The study had shown an ideal urine specimen is that which is sensitive to the underlying pathology of a UTI. It is also a urine specimen that is easy to collect. The direct void is the recommended method of choice but should be accompanied with microscopy. Uroplakin staining should be initiated to further detect the positive presence of uroepithelial cells when distinguishing the difference between urinary contamination.

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