Sensitivity of Gram stain in the diagnosis of urethritis in men.
BACKGROUND
Acute urethritis is among the most common types of sexually transmitted diseases in men. The diagnosis usually requires microscopic evidence of urethritis, but sometimes urethral pathogens are detected in asymptomatic men without such evidence. The aims of this study were to assess the sensitivity of Gram stain in men with urethral symptoms and to relate it to the microorganisms isolated.


METHODS
Between January 2006 and December 2007, 491 urethral samples were analysed. The authors assessed the presence of leukocytes by Gram stain and tested specifically for Chlamydia trachomatis, Ureaplasma urealyticum, Mycoplasma hominis and Trichomonas vaginalis, as well as analysing the results of conventional culture.


RESULTS
The percentages of positive samples as a function of Gram category were two or less polymorphonuclear leukocytes (PMNLs)/high-power field (HPF) 25% (92/364), three to four PMNLs/HPF 32% (18/57) and five or more PMNLs/HPF 54% (38/70). Classing samples with more than two PMNLs/HPF as positive, the sensitivity, specificity and positive likelihood ratio for Gram stain were 38% (95% CI 30 to 46), 79% (95% CI 75 to 84) and 1.8 (95% CI 1.4 to 2.4), respectively. On the other hand, taking as positive five or more PMNLs/HPF, the sensitivity, specificity and positive likelihood ratio for Gram stain were 26% (95% CI 18 to 33), 91% (95% CI 87 to 94) and 2.7 (95% CI 1.8 to 4.2), respectively. The sensitivity of Gram stain to Neisseria gonorrhoeae, Chlamydia trachomatis and Ureaplasma urealyticum were 80% (95% CI 64 to 96), 23% (95% CI 8 to 39) and 11% (95% CI 2 to 20), respectively.


CONCLUSIONS
The low sensitivity of Gram stain means that negative results do not exclude the presence of urethritis in symptomatic patients.
Laboratorio C.E.P, Pontones, Madrid, Spain. m.a.orellana@jv.e.telefonica.net
M Angeles
MA
Orellana
M Luisa
ML
Gómez-Lus
David
D
Lora
D000293:Adolescent; D000328:Adult; D000368:Aged; D004396:Coloring Agents; D003430:Cross-Sectional Studies; D005840:Gentian Violet; D016905:Gram-Negative Bacterial Infections / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009504:Neutrophils; D010619:Phenazines; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D014245:Trichomonas Infections / Q000175:diagnosis*; D014526:Urethritis / Q000175:diagnosis*; D055815:Young Adult
D004396:Coloring Agents; C035863:Gram's stain; D010619:Phenazines; D005840:Gentian Violet