Acridine orange as a screen for organisms in clinical specimens and comparison with gram's stain

We compared the result of acridine orange and Gram's stains with the results of culture for 202 wound swabs and 188 fluid specimens. Cerebrospinal fluid was excluded from the study. Acridine orange was more sensitive and less specific than Gram's stain compared with findings that have been previously reported. A difference in the sensitivity was observed between the two stains and between the types of specimens examined themselves. The sensitivity of acridine orange and Gram's stains was 83% and 49% for swabs and 66% and 45% for fluids, respectively. The negative predictive values for acridine orange and Gram's stains were 60% and 40% for swabs and 84% and 81% for fluids, respectively. Overall, the sensitivity for acridine orange and Gram's stains was 75% and 64% with negative predictive values of 75% and 63%, respectively; specificity was 75% (acridine orange) and 97% (Gram's stain) and did not differ significantly between the two specimen types. Acridine orange was cleaner, faster, easier to perform and read, and less costly than Gram's stain for screening purposes. Slides that were positive by acridine orange staining should be stained with Gram's stain for specificity and for the Gram's-stain reaction report. Acridine orange is recommended for screening smears, with positive results confirmed by Gram's stain.