Polymorph count for predicting non-gonococcal urethral infection: a model using Chlamydia trachomatis diagnosed by ligase chain reaction
- 1Department of Genitourinary Medicine, Camden Primary Care Trust, Mortimer Market Centre, London WC1E 6AU, UK
- 2Centre for Sexual Health and HIV Research, Department of Primary Care and Population Sciences, Royal Free and University College Medical School, University College London, London WC1E 6AU, UK
- 3Department of Clinical Microbiology, University College London Hospitals NHS Trust, London WC1E 6DB, UK
- Correspondence to: Dr T Sadiq The Courtyard Clinic, Department of Cellular and Molecular Medicine, St George’s Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK;
- Accepted 20 November 2003
Background/objectives: The criteria for the diagnosis of non-gonococcal urethritis (NGU) on a Gram stained urethral smear are derived from previous studies which used culture as a diagnostic test for Chlamydia trachomatis. Our objectives were (1) to re-assess the relation between urethral polymorph count and C trachomatis infection, using ligase chain reaction (LCR) as the diagnostic test; and (2) to assess other possible predictors of C trachomatis infection such as symptoms, signs, demographic and behavioural variables.
Methods: We collected data from 363 men consecutively attending a genitourinary medicine clinic (excluding those with gonorrhoea and follow up visits) who had a urethral smear and a urethral LCR test for C trachomatis. The sensitivity and specificity of a discrete cut off in urethral polymorphonuclear leucocyte (PMNL) count as a diagnostic test for chlamydia urethritis were calculated. The associations between other variables, such as age and symptoms, and this infection were also estimated.
Results: 8% of men had C trachomatis infection and 26% of men had a PMNL count of 5 or more. Of those men with chlamydia 37% did not have NGU; 20% of men with NGU had chlamydia. Adjusted odds ratios for risk of chlamydial infection were significant for age less than 30 relative to 40 years and over (adj OR 13.6; 95% confidence interval 1.69 to 110), a PMNL count of 20 or more (6.56; 2.15 to 20.0), a PMNL count of 5–19 (3.59; 1.41 to 9.15), and the symptom of dysuria (3.27; 1.32 to 8.08). However a PMNL count of 5 or more was only 63% sensitive and 77% specific for C trachomatis infection. No association between sexual behaviour and chlamydial infection was found in this setting.
Conclusions: The PMNL count is associated with presence of chlamydial infection but a large proportion of men with chlamydia have PMNL counts below the recommended cut off for a diagnosis of NSU. Lower age and the presence of symptoms may be as predictive as the urethral polymorph count for chlamydial urethritis and possibly for other urethral infections.
- LCR, ligase chain reaction
- NAATs, nucleic acid amplification tests
- NGU, non-gonococcal urethritis
- PID, pelvic inflammatory disease
- PMNL, polymorphonuclear leucocytes