Table 2 Diagnostic performance of ETA using quantitative culture obtained from standardised BAL as the reference, with growth at >10⁴ CFU/ml defining “true VAP”

	Sensitivity (%)	Specificity (%)	PPV (%)	NPV (%)	+LR	–LR
Qualitative ETA cultures	90	14	21	85	1	0.6
Quantitative ETA cultures	72	55	30	88	1.6	0.5

Qualitative ETA is growth of any organism; quantitative ETA is growth of any organism at >10⁶ colony-forming units (CFU)/ml.20 A likelihood ratio is a likelihood that a person with a positive (or negative) test has the disease in question; further detail can be found in Strauss et al.25
BAL, bronchoalveolar lavage; ETA, endotracheal aspirate; NPV, negative predictive value; PPV, positive predictive value; +LR, positive likelihood ratio; –LR, negative likelihood ratio; VAP, ventilator-associated pneumonia.