THE DIAGNOSTIC-VALUE OF GRAM STAIN FOR INITIAL IDENTIFICATION OF THE ETIOLOGIC AGENT OF PERITONITIS IN CAPD PATIENTS

Objective: To evaluate the effectiveness of the Gram stain in the init ial diagnosis of the etiologic agent of peritonitis in continuous ambu latory peritoneal dialysis (CAPD). Design: Retrospective study analyzi ng the sensitivity (S), specificity (SS), positive predictive value (PV), and negative predictive value (-PV) of the Gram stain relating to the results of cultures in 149 episodes of peritonitis in CAPD. The d ata were analyzed in two studies. In the first, only the cases with de tection of a single agent by Gram stain were taken (Study 1). In the s econd, only the cases with two agents in Gram stain were evaluated (St udy 2). Setting: Dialysis Unit and Laboratory of Microbiology of a ter tiary medical center. Patients: Sixty-three patients on regular CAPD w ho presented one or more episodes of peritonitis from May 1992 to May 1995. Results: The positivity of Gram stain was 93.2% and the sensitiv ity was 95.7%. The values of S, SS, +PV, and -PV were respectively: 94 .9%, 53.5%, 68.3%, and 90.9% for gram-positive cocci and 83.3%, 98.8%, 95.2%, and 95.6% for gram-negative bacilli. The association of grampo sitive cocci plus gram-negative bacilli were predictive of growth of b oth in 6.8%, growth of gram-positive cocci in 13.7%, and growth of gra m-negative bacilli in 72.5%. Conclusions: The Gram stain is a method o f great value in the initial diagnosis of the etiologic agent of perit onitis in CAPD, especially for gram-negative bacilli.