IS PROTECTED SPECIMEN BRUSH A REPRODUCIBLE METHOD TO DIAGNOSE ICU-ACQUIRED PNEUMONIA

Protected specimen brush (PSB) is considered to be one of the standard methods for the diagnosis of ventilator-associated pneumonia, but to our knowledge, intraindividual variability in results has not been rep orted previously. Purpose: To compare the results of two PSB performed in the same subsegment on patients with suspected ICU-acquired pneumo nia (IAP). Study design: Between October 1991 and April 1992, each mec hanically ventilated patient with suspected LAP underwent bronchoscopy with two successive PSB in the lung segment identified as abnormal on radiographs. Results of the two PSB cultures were compared using 10(3 ) cfu/ml cutoff for a positive result. Four definite diagnoses were es tablished during the follow up: definite pneumonia, probable pneumonia , excluded pneumonia, and uncertain pneumonia. Population: Forty-two e pisodes in 26 patients were studied; 60 percent of patients received p rior antibiotic therapy. Thirty-two microorganisms were isolated from 24 pairs of PSB. Definite diagnosis was definite pneumonia in 7, proba ble pneumonia in 8, excluded pneumonia in 17, and uncertain pneumonia in 10 cases. Results: The PSB recovered the same microorganisms and ar gued for a good qualitative reproducibility. The distinction of positi ve and negative results on the basis of the 10(3) cfu/ml classic thres hold was less reproducible. For 24 percent of the microorganisms recov ered and in 16.7 percent of episodes of suspected IAP, the two consecu tive samples gave results spread out on each side of the 10(3) cfu/ml cutoff. Discordance was higher when definite diagnosis was certain or probable than when diagnosis was excluded (p=0.015). There was no stat istical effect of the order of samples between the two specimens for b acterial index and microorganism concentrations. Conclusion: These fin dings argue for the poor repeatability of PSB in suspected LAP and que stion the yield of the 10(3) cfu/ml threshold. In attempting to diagno se LAP, the results of PSB must be interpreted with caution considerin g the intraindividual variability.