Polymorph count for predicting non-gonococcal urethral infection: a model using Chlamydia trachomatis diagnosed by ligase chain reaction.
OBJECTIVE
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.
Haddow
L J
LJ
Department of Genitourinary Medicine, Camden Primary Care Trust, Mortimer Market Centre, London WC1E 6AU, UK.
Bunn
A
A
Copas
A J
AJ
Gilson
R
R
Prince
M
M
Ridgway
G L
GL
Sadiq
S T
ST
D000293:Adolescent; D000328:Adult; D000368:Aged; D002690:Chlamydia Infections / Q000175:diagnosis*; D002692:Chlamydia trachomatis; D006801:Humans; D007958:Leukocyte Count; D022521:Ligase Chain Reaction / Q000379:methods / Q000592:standards; D008297:Male; D008875:Middle Aged; D009504:Neutrophils; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D014522:Urethral Diseases / Q000175:diagnosis*