Recalibrating the Gram Stain Diagnosis of Male Urethritis in the Era of Nucleic Acid Amplification Testing

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Criteria for diagnosis of male urethritis based on a Gram-stained smear (GSS) of urethral discharge were developed before the era of nucleic acid amplification testing (NAAT) for Neisseria gonorrhoeae (Ng) and Chlamydia trachomatis (Ct) and may be too stringent when considering the higher sensitivity of NAAT.


To evaluate Ct and Ng positivity at different strata of polymorphonuclear cells (PMN) per high power field (hpf) GSS microscopy.


A retrospective analysis of the electronic medical record system of the Denver Metro Health Clinic between March 1, 2005 and December 31, 2010; all men with a GSS test during this period had an NAAT for Ct and Ng and had GSS results recorded at 1 PMN/hpf increments.


A total of 13,520 GSS were available for analysis. For Ct, a statistically significant trend was observed along the PMN/hpf incremental spectrum, and a significant increase in positivity was observed between the 1 and 2 PMN/hpf strata (from 6.5% to 16.2%). For men diagnosed with Ng, no such trend was observed, and >95% of GSS results fell in the >10 strata. A subanalysis to control for laboratory technician variance and difference in NAAT technology showed similar results.


Our data support lowering the diagnostic criteria of the GSS diagnosis of male urethritis to ≥2 PMN/hpf. At this level, the Ct positivity (16.2%) is similar or higher than positivity in men who receive presumptive chlamydia treatment as a contact to patients diagnosed with gonorrhea, pelvic inflammatory disease, or mucopurulent cervicitis.

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