Microscopy of stained urethral smear in male urethritis; which cutoff should be used?

Centers for Disease Control and Prevention lowered recently the cutoff value for the microscopical diagnosis of male urethritis to ≥2 polymorphonuclear leucocytes/high power field. Our data suggest a cutoff of ≥10 polymorphonuclear leucocytes/high power field. A standardization of urethral smear microscopy seems impossible.

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Background: The microscopical diagnosis of male urethritis was recently questioned by Rietmeijer and Mettenbrink, lowering the diagnostic criteria of the diagnosis to ≥2 polymorphonuclear leucocytes (PMNL) per high power field (HPF), and adopted by Centers for Disease Control and Prevention in their 2015 STD Treatment Guidelines. The European Non-Gonococcal Urethritis Guideline advocates a limit of ≥5 PMNL/HPF.

Objective: To determine if syndromic treatment of urethritis should be considered with a cutoff value of ≥2 PMNL/HPF in urethral smear.

Methods: The design was a cross-sectional study investigating the presence and degree of urethritis relative to specific infections in men attending an STI clinic as drop-in patients.

Results: The material included 2 cohorts: a retrospective study of 13,295 men and a prospective controlled study including 356 men. We observed a mean chlamydia prevalence of 2.3% in the 0–9 stratum, and a 12-fold higher prevalence (27.3%) in the strata above 9. Of the chlamydia cases, 89.8% were diagnosed in strata above 9. For Mycoplasma genitalium, the prevalence was 1.4% in the 0–9 stratum and 11.2% in the stratum ≥10, and 83.6% were diagnosed in strata above 9. For gonorrhea, a significant increase in the prevalence occurred between the 0–30 strata and >30 strata from 0.2% to 20.7%. The results of the prospective study were similar.

Conclusions: Our data do not support lowering the cutoff to ≥2 PMNL/HPF. However, a standardization of urethral smear microscopy seems to be impossible. The cutoff value should discriminate between low and high prevalence of chlamydia, mycoplasma, and gonorrhea to include as many as possible with a specific infection in syndromic treatment, without overtreating those with few PMNL/HPF and high possibility of having nonspecific or no urethritis.

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