Poor sensitivity and consistency of microscopy in the diagnosis of low grade non-gonococcal urethritis

Abstract

Objectives: To determine the reliability of the diagnosis of non-gonococcal urethritis (NGU), and the variation between and within microscopists, from urethral smears at a large London genitourinary medicine clinic. Methods: A senior microscopist (SM) preselected 60 Gram stained urethral smear slides, 20 negative (,5 polymorphs/hpf), 20 low grade NGU (5-20 p/hpf), and 20 high grade NGU (.20 p/hpf). Ten experienced microscopists, blinded to these initial grades, examined all slides giving each a polymorph score. After relabelling and randomly changing their order, the slides were re-examined by the same microscopists. Finally, the SM determined whether the study had resulted in loss of cells from any of the slides. The SM's initial grading and the consensus among microscopists provide two gold standards for analysis. Results: Nine low grade and five high grade slides were removed from analysis because of loss of cells. By SM standard, considering microscopists' readings as simply non-NGU (,5 p/hpf) or NGU (>5 p/hpf), 97% from negative slides were correct (variation 93-100 across microscopists), 68% from low grade slides (45-95), and 94% from high grade slides (83-100). Consistency between repeat readings by the same microscopist was 96% for negatives, 75% for low grade and 89% for high grade slides. Results were similar by consensus standard. Conclusions: There was considerable variation between and within microscopists in the diagnosis of NGU. Sensitivity was strongly related to grade of urethritis, with an appreciable proportion of low grade urethritis falsely diagnosed as negative. With increasing attendances for sexual health screening, a false positive rate of only 3% may lead to many false diagnoses.

New assay for Gardnerella vaginalis loads correlates with Nugent scores and has potential in the diagnosis of bacterial vaginosis

“…The lack of a reference qPCR threshold and the indeterminate intermediate range of the Nugent score make it impossible to undertake a fully meaningful head-to-head comparison and clearly indicate the need for better discrimination in establishing a diagnosis of BV (Smith et al, 2003;Srinivasan et al, 2013). All BV-confirmed samples in the study had a minimal G. vaginalis load of 10 7 copies ml…”

“…Whilst clue cells (epithelial cells demonstrating a studded appearance due to the attachment of large numbers of G. vaginalis) aid in the diagnosis of BV, their absence in women with an intermediate flora decreases the specificity and positive predictive value of the Nugent score (Amsel et al, 1983;Nugent et al, 1991). Microscopy also lacks sensitivity compared with molecular techniques (Kubista et al, 2006;Smith et al, 2003;Srinivasan et al, 2013), and is further compromised when the Gram stain's reliability is reduced in the presence of antibiotics or when BV is associated with an increased composition of bacterial species such as Mycoplasma and Ureaplasma, which lack a defined cell wall (Rosenstein et al, 1996;Sha et al, 2005). G. vaginalis load clearly increases in women with BV (Balashov et al, 2014), suggesting that quantification would be useful in the diagnosis of this condition.…”

The Ballseye programme: a mixed-methods programme of research in traditional sexual health and alternative community settings to improve the sexual health of men in the UK

“…However, the consequence of men passing urine < 2 hours prior to testing would have weakened rather than strengthened the associations that we describe. Interobserver variation in urethral smear microscopy is well recognised 52 and, although we cannot exclude this, all of our microscopists adhere to regular audits and quality control processes. It is also possible that some of these men actually had chlamydial urethritis but a false-negative urine test, although the risk is small.…”

“…50 There is also significant intra-and inter-observer variability in reading urethral smear Gram stains. 51,52 The epidemiology of infections will vary between the geographical locations of the studies (Scotland 47 and south of England 48 ) and when they were conducted (between 2002 and 2007), meaning that the findings are not directly transferable to current populations.…”

2009 European Guideline on the Management of Male Non-gonococcal Urethritis

“…There is significant inter-observer and intra-observer error in performing and reading urethral slides and counting PMNLs, especially in samples with low-grade inflammation. 3,4 In many men with urethritis, a known pathogen is not isolated. 5 -8 Up to one-third of men infected with either C. trachomatis or M. genitalium will not have an excess of PMNLs, 7,9 -13 the sensitivity of smear (!5 PMNLs) being far better in the case of an overt discharge, variations being furthermore dependent on populations and techniques of sampling.…”