Predictive value of BAL cell differentials in the diagnosis of interstitial lung diseases

The current authors aimed to quantify how the likelihood for a given diagnosis changes with the knowledge of bronchoalveolar lavage (BAL) cell differentials. As an initial estimate (a priori probability), frequencies of final diagnoses were taken. Using categorisations for cell differentials, a posteriori probabilities were then derived for each disease, according to Bayes. The analysis was performed in three of five groups of diagnoses suspected prior to BAL: interstitial lung disease (ILD; n=710), inflammatory disease (n=583), or lung tumour mimicking ILD (n=455). Overall, out of 1,971 patients, 18.3% had sarcoidosis, 7.7% usual interstitial pneumonia (UIP), 4.4% extrinsic allergic alveolitis (EAA), and 19.0% tumours. In the group with suspected ILD, the likelihood for sarcoidosis increased from 33.7 to 68.1% when lymphocyte numbers were 30-50% and granulocyte numbers were low; the likelihood for UIP increased from 15.8 to 33.3% when lymphocyte numbers were