Interpreting the sputum gram stain report

A retrospective review of patient records was performed to determine the st atistical relationship between sputum Gram stain and culture results in adu lt men at a Veterans Affairs Medical Center in the Midwest Gram stain resul ts from 1996 were statistically compared with culture results for 2,105 spu tum specimens. Positive predictive values for common Gram stain morphotypes and their corresponding organisms varied from 7.1% to 90.6%. In some insta nces, the absence of a particular Gram stain morphotype (eg, gram-negative diplococci) was more predictive of the absence of an organism in culture (e g, Moraxella catarrhalis) than its presence. Also, Gram stain reports notin g the presence of gram-negative bacilli were not predictive of cultures wit h gram-negative bacilli potential respiratory pathogens (positive predictiv e values 32.4%-54.9%). rn conclusion, Gram stain results often were not acc urate predictors of sputum culture results. One way to improve agreement be tween Gram stain and culture results is to develop Gram stain interpretatio n guidelines based on statistical relationships between stain and culture.