The study aimed to determine the diagnostic usefulness of the genital Gram stain in an emergency department (ED) population.

A linked-query of an urban, tertiary-care, university- affiliated hospital laboratory database was conducted for all completed Chlamydia trachomatis and Neisseria gonorrhoeae DNA probes, Trichomonas vaginalis wet preps, and genital Gram stains performed on ED patient visits between January and December 2004. Positive criteria for a Gram stain included greater than 10 white blood cells per high-power field, gram-negative intracellular/extracellular diplococci (suggesting N gonorrhoeae), clue cells (suggesting T vaginalis), or direct visualization of T vaginalis organisms. DNA probes were used as the gold standard definition for N gonorrhoeae and C trachomatis infection.

Of 1511 initially eligible ED visits, 941 were analyzed (genital Gram stain and DNA probe results both present), with a prevalence of either C trachomatis or N gonorrhoeae of 11.4%. A positive genital Gram stain was 75.7% sensitive and 43.3% specific in diagnosing either C trachomatis and/or N gonorrhoeae infection, and 80.4% sensitive and 32.2% specific when the positive cutoff was lowered to more than 5 white blood cells/high-power field. No Gram stains were positive for T vaginalis (with 47 positive wet mounts), and clue cells were noted on 117 Gram stains (11.6%).

Gram stains in isolation lack sufficient diagnostic ability to detect either C trachomatis or N gonorrhoeae infection in the ED.