Statistical analysis. In accord with previous studies (1, 14, 15, 21, 22) of quantitative bacteriology of BAL cultures, a bacterial density of >104cfu/ml was considered as 'POSITIVE' for VAP and those episodes were referred to as 'DEFINITE VAP' episodes. The organisms isolated on blood culture were compared against the organisms isolated from the cultures of various tracheobronchial techniques using the chi square test. Analysis was also done for any relation between the semi-quantitation of PMN on gram stain and cultures of the lower tracheobronchial secretions. Taking BAL colony counts of ≥ 104 cfu/ml as the reference standard, the other three methodologies - ETA, BBS and blind BAL were analyzed and their receiver operating curves (ROC) were plotted and the area under the curve were also obtained. Following this, the sensitivities, specificities, positive and negative predictive values (PPV, NPV) and accuracies at various cut off values of colony counts for all the above mentioned techniques were calculated. Concordance between different diagnostic methods was analyzed using kappa score. P value less than 0.05 was considered significant.