Table 2– Receiver-operating characteristic (ROC) analysis for plasma and sputum biomarkers
Overlap versus COPDOverlap versus asthmaCOPD versus asthmaOverlap versus NSCOPD versus NS
Plasma
 sRAGE
  AUC (95% CI)0.570 (0.397–0.743)0.719 (0.553–0.884)0.737 (0.616–0.858)0.703 (0.513–0.893)0.703 (0.564–0.842)
  Optimal threshold pg·mL−1>673.9<758.2<903.5<768.9<819.7
  Sensitivity/specificity0.643/0.5310.714/0.8120.719/0.6560.714/0.7730.625/0.727
  p-value0.4520.0190.0030.0430.012
 SP-A
  AUC (95% CI)0.607 (0.424–0.790)0.759 (0.608–0.910)0.682 (0.550–0.813)0.935 (0.857–1.013)0.897 (0.810–0.985)
  Optimal threshold ng·mL−1>39.5>39.0>33.5>29.0>28.5
  Sensitivity/specificity0.643/0.5620.643/0.7500.656/0.6250.857/0.9130.844/0.913
  p-value0.2520.0060.0130.000010.000001
Sputum
 MPO
  AUC (95% CI)0.618 (0.362–0.873)0.732 (0.492–0.972)0.726 (0.589–0.862)0.733 (0.517–0.950)0.736 (0.568–0.904)
  Optimal threshold μg·mL−1>14.9>13.0>10.5>12.5>5.0
  Sensitivity/specificity0.600/0.6070.700/0.8800.679/0.6400.700/0.7220.893/0.667
  p-value0.2740.0340.0050.0440.007
 NGAL
  AUC (95% CI)0.708 (0.502–0.914)0.818 (0.635–1.001)0.697 (0.555–0.839)0.869 (0.728–1.009)0.781 (0.634–0.928)
  Optimal threshold μg·mL−1>4.4>4.2>3.5>4.2>2.0
  Sensitivity/specificity0.727/0.7140.818/0.8000.643/0.7200.818/0.8890.857/0.667
  p-value0.0460.0030.0140.0010.001
  • COPD: chronic obstructive pulmonary disease; NS: nonsmoker; sRAGE: soluble receptor for advanced glycation end-products; AUC: area under the curve; SP-A: surfactant protein A; MPO: myeloperoxidase; NGAL: neutrophil gelatinase-associated lipocalin.