Question
What is the association between the number of polymorphonuclear leukocytes in a high power microscopic field (PMNL/hpf) of a Gram-stained urethral smear and the detection of C. trachomatis in a urethral swab using a ligase chain reaction assay (LCR)?

Design
The relationship between urethral polymorph count and C. trachomatis infection in men, as determined using ligase chain reaction, and other possible predictors of C. trachomatis infection such as signs and symptoms and demographic and behavioral characteristics were determined.  
Participants
Three hundred sixty-three men having STI screens were tested.  Men who had gonococcal urethritis were excluded.  The median age was 31.9 years (range = 18-76 years), 82% were white, 50% were men who have sex with men.  Sixty-one (16.8%) and 36 (9.9%) presented with or complained of dysuria and discharge, respectively.   

Description of Tests and Diagnostic Standard
Urethral swabs were collected for preparation of smears and for detection of C. trachomatis.  Smears were Gram stained and the number of PMNL/hpf, averaged over 5 fields, was determined.  The presence of 5 or more PMNL/hpf was considered positive for urethritis.  C. trachomatis was detected using the LCR assay (LCx, Abbott Laboratories, Chicago, IL).  

Main Outcome Measures
The sensitivity and specificity of a discrete cut-off in urethral PMNL count as a diagnostic test for chlamydia urethritis were calculated.    

Main Results
The prevalence of non-gonococcal urethritis diagnosed on urethral smear was 26.4% (96/363) and the prevalence of C. trachomatis by LCR was 8.3% (30/363).  The prevalence of C. trachomatis was 4.1% in men with less than 5 PMNL/hpf compared to 31.0% in men with 20 or more PMNL/hpf (p<0.001).  Thirty-seven percent of men with chlamydial infection diagnosed by LCR had no microscopic evidence of urethritis.  Diagnosis by a urethral PMNL count of 5 or more had a sensitivity, specificity, positive predictive value, and negative value for urethral chlamydia of 63.3%, 76.9%, 19.8%, and 95.9%, respectively.  On multivariate analysis, the strongest associations with chlamydial infection were age less than 30 years (adjusted odds ratio (OR) = 13.6), PMNL/hpf of 5 to 19 (OR = 3.59) and 20 or more (OR = 6.56), and dysuria (OR = 3.27).  The presence of discharge had no additional predictive power once a history of dysuria was elicited.  

Authors’ Conclusions
Symptoms of dysuria and age were as strongly associated with chlamydia infection as urethral polymorph count and should be incorporated into the predictive algorithm of urethral infection.

 
Source of funding:  None given.

For correspondence:  S. T. Sadiq, The Courtyard Clinic, Department of Cellular and Molecular Medicine, St. George’s Hospital Medical School, Cranmer Terrace, London, SW17 0RE, UK.  E-mail address: s.sadiq@sghms.ac.uk.