Bafadhel et al collected procalcitonin and CRP on 161 people admitted for COPD exacerbations, 96 for asthma exacerbations, and 62 for pneumonia (groups were discriminated by presence of consolidation on chest film), at 2 UK hospitals. The assays performed extremely well (area under the curve >0.93 for each) at differentiating pneumonia from non-infectious causes of dyspnea. By definition, performance varied according to the threshold values used for the tests -- the best values are yet to be determined, and may vary between different labs/manufacturers. CHEST 2011;139:1410-1418.
However, among 65 people intubated for aspiration syndromes at SUNY-Buffalo, procalcitonin did not differentiate between those with positive BAL cultures ("aspiration pneumonia") and negative BAL cultures ("aspiration pneumonitis"). BAL was collected in <6 hours, and all patients received appropriate antibiotics, but time-to-antibiotics was not reported by El-Solh et al. Crit Care Med 2011;39:1251-1256.