Correlation between gram stains and culture results in patients with corneal ulcers

Purpose. To correlate gram stains and culture results from patients with corneal ulcers. Methods. Charts of 51 patients identified from the microbiology laboratory files from January through June 1995 with a clinical diagnosis of corneal ulcer were reviewed. Gram stains and culture results were compared. Results. 44/51 (86%) patients (44 eyes) had both gram stain and cultures performed. The sensitivity and specificity of the gram stain were 56% and 100%, respectively, with a high positive predictive value (100%), but a low negative predictive value (33%). The gram stain reaction correlated with the organism identified by culture in all cases (100%). Culture + Culture - Gram Stain Positive 20 pts. 0 pts. Gram Stain 16 pts. 8 pts Negative Conclusions. Gram stains have a high positive predictive value and are reliable predictors of the ultimate bacterial isolute. Therefore, a positive gram stain result can reliably guide initial treatment until cultures and sensitivities are available. Conversely, a negative gram stain should not be used to rule out bacterial ulcers, because false negative results occurred in 44% of cases. Both gram stain and culture should be performed routinely in the management of corneal ulcers.