Bronchoalveolar lavage cell differential in the diagnosis of sarcoid interstitial lung disease. Likelihood ratios...

With the use of a microcomputer, the authors prospectively stored the bronchoalveolar lavage (BAL) cell differential counts from 208 patients undergoing initial evaluation for chronic interstitial lung disease. Sarcoidosis subsequently was diagnosed in 46% of these patients; the remainder had several other etiologies of their lung disease. The BAL lymphocyte count did not allow for clear separation between these two groups. To facilitate the interpretation of the BAL percent lymphocyte data, the authors applied a modification of Bayes' theorem to calculate likelihood ratios for the differential diagnosis of sarcoidosis versus other interstitial lung disease. These values ranged from 0.15 for patients with less than 6% lymphocytes to 3.5 when more than 40% lymphocytes were found. Similar results were obtained with a subsequent, independently analyzed group of 46 patients. To provide a more meaningful interpretation of the BAL fluid lymphocyte count, the authors designed a reporting scheme that includes both a written description and a graphic representation of the likelihood ratio. Prospective collection of data using microcomputers should extend this useful form of reporting to additional laboratory studies.