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Polymorph count for predicting non-gonococcal urethral infection: a model using Chlamydia trachomatis diagnosed by ligase chain reaction
  1. L J Haddow1,
  2. A Bunn1,
  3. A J Copas2,
  4. R Gilson2,
  5. M Prince3,
  6. G L Ridgway3,
  7. S T Sadiq2
  1. 1Department of Genitourinary Medicine, Camden Primary Care Trust, Mortimer Market Centre, London WC1E 6AU, UK
  2. 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
  3. 3Department of Clinical Microbiology, University College London Hospitals NHS Trust, London WC1E 6DB, UK
  1. 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;


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.

  • non-specific urethritis
  • urethra
  • specificity
  • chlamydia
  • LCR, ligase chain reaction
  • NAATs, nucleic acid amplification tests
  • NGU, non-gonococcal urethritis
  • PID, pelvic inflammatory disease
  • PMNL, polymorphonuclear leucocytes

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