Circulating CRP and calprotectin to diagnose CF pulmonary exacerbations

Cystic fibrosis (CF) pulmonary exacerbations (PEx) remain underdiagnosed by CF clinicians. Serum C-reactive protein (CRP) and calprotectin are inflammatory biomarkers that have the potential to aid in the diagnosis of PEx. 19 subjects (56 stable, 46 PEx visits) from a longitudinal study were included and the diagnostic performance of absolute and fold-change CRP and calprotectin cut-offs to discriminate stable and PEx visits was assessed. Based on Youden's index, optimal absolute and fold-change thresholds to identify PEx were 9.5 mg/L (Sn 76%, Sp 73%; AUC 0.76) and 2.2-fold (Sn 50%, Sp 96%; AUC 0.78) for CRP and 8.1 mg/L (Sn 61%, Sp 79%; AUC 0.72) and 1.3-fold (Sn 57%, Sp 88%; AUC 0.74) for calprotectin. A step-wise algorithm was able to improve diagnostic performance (Sn 80%; Sp 88%). CRP and calprotectin could discriminate stable vs. PEx visits with good performance and appear promising as diagnostic biomarkers but further validation studies are required prior to implementing these diagnostic thresholds.