Abstract
Introduction and hypothesisUrinary dipsticks and culture analyses of a mid-stream urine specimen (MSU) at 105 cfu ml−1 of a known urinary pathogen are considered the gold standard investigations for diagnosing urinary tract infection (UTI). However, the reliability of these tests has been much criticised and they may mislead. It is now widely accepted that pyuria (≥1 WBC μl−1) detected by microscopy of a fresh unspun, unstained specimen of urine is the best biological indicator of UTI available. We aimed to scrutinise the greater potential of symptoms analysis in detecting pyuria and UTI.MethodsLower urinary tract symptom (LUTS) descriptions were collected from patients with chronic lower urinary tract symptoms referred to a tertiary referral unit. The symptoms informed a 39-question inventory, grouped into storage, voiding, stress incontinence and pain symptoms. All questions sought a binary yes or no response. A bespoke software package was developed to collect the data. The study was powered to a sample of at least 1,990 patients, with sufficient power to analyse 39 symptoms in a linear model with an effect size of Cohen’s f2 = 0.02, type 1 error probability = 0.05; and power (1-β); 95% where β is the probability of type 2 error). The inventory was administered to 2,050 female patients between August 2004 and November 2011. The data were collated and the following properties assessed: internal consistency, test–retest reliability, inter-observer reliability, internal responsiveness, external responsiveness, construct validity analysis and a comparison with the International Consultation on Incontinence Modular Questionnaire for female lower urinary tract symptoms (ICIQ-FLUTS). The dependent variable used as a surrogate marker of UTI was microscopic pyuria. An MSU sample was sent for routine culture.ResultsThe symptoms proved reliable predictors of microscopic pyuria. In particular, voiding symptoms correlated well with microscopic pyuria (χ2 = 88, df = 1, p < 0.001). The symptom inventory has significant psychometric characteristics as below: test–retest reliability: Cronbach’s alpha was 0.981; inter-observer reliability, Cronbach’s alpha was 0.995, internal responsiveness F = 221, p < 0.001, external responsiveness F = 359, df = 5, p < 0.001. The correlation coefficients for the domains of the ICIQ-FLUTS were around R = 0.5, p < 0.001.ConclusionThis symptoms score performed well on the standard, psychometric validation. The score changed in response to treatment and in a direction appropriate to the changes in microscopic pyuria. It correlated with measures of quality of life. It would seem to make a good candidate for monitoring treatment progress in ordinary clinical practice.
Highlights
Introduction and hypothesisUrinary dipsticks and culture analyses of a mid-stream urine specimen (MSU) at 105 cfu ml−1 of a known urinary pathogen are considered the gold standard investigations for diagnosing urinary tract infection (UTI)
The correlation coefficients for the domains of the Incontinence Questionnaire (ICIQ)-FLUTS were around R = 0.5, p < 0.001
The score changed in response to treatment and in a direction appropriate to the changes in microscopic pyuria
Summary
Urinary dipsticks and culture analyses of a mid-stream urine specimen (MSU) at 105 cfu ml−1 of a known urinary pathogen are considered the gold standard investigations for diagnosing urinary tract infection (UTI). Urinalysis by dipstick and/or midstream urine culture (MSU) is the first investigation of the patient presenting with lower urinary tract symptoms (LUTS). The MSU is still considered the gold standard diagnostic test for UTI. It relies on isolating 105 cfu ml−1 of a known urinary pathogen, using aerobic culture with a Enterobacteriaceae-selective media. This was first described by Kass [1] after studying patients with chills, fever, flank pain and dysuria. The dipstick has been validated against a standard of 105 cfu ml−1 of a known urinary pathogen
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