Individual biomarkers and biomarker combinations
| Biomarker/combination Cut-point | Sensitivity (95% CI) | Specificity (95% CI) | PPV (95% CI) | NPV (95% CI) | +LR (95% CI) | −LR (95% CI) | PTP (%) (95% CI) |
|---|---|---|---|---|---|---|---|
| IL-1β 17 pg/mL | 96.2% (87.2 to 99.0) | 43.3% (33.9 to 53.2) | 0.48 (0.39 to 0.58) | 0.96 (0.85 to 0.99) | 1.70 (1.41 to 2.04) | 0.09 (0.02 to 0.35) | 4.5 (1.3 to 5.1) |
| IL-8 382 pg/mL | 98.1% (90.1 to 99.7) | 24.7% (17.2 to 34.2) | 0.42 (0.33 to 0.50) | 0.96 (0.80 to 0.99) | 1.30 (1.16 to 1.47) | 0.08 (0.01 to 0.55) | 4 (0.7 to 19.5) |
| MMP-8 160 ng/mL | 100% (93.3 to 100.0) | 5.2% (1.7 to 11.6) | 0.37 (0.29 to 0.45) | 1.0 (0.57 to 1.0) | 1.05 (1.01 to 1.10) | 0.0 (NE) | 0.0 (0.0 to 0.43) |
| MMP-9 296 ng/mL | 96.2% (87.0 to 99.5) | 43.4% (33.3 to 53.7) | 0.48 (0.38 to 0.58) | 0.96 (0.85 to 0.97) | 1.70 (1.41 to 2.04) | 0.09 (0.02 to 0.35) | 4.5 (3.9 to 15.3) |
| HNE 161 ng/mL | 98.1% (89.9 to 99.9) | 34.0% (24.7 to 44.3) | 0.45 (0.36 to 0.54) | 0.97 (0.85 to 0.98) | 1.49 (1.28 to 1.72) | 0.06 (0.01 to 0.39) | 2.9 (1.9 to 15.0) |
| IL-1β/IL-8 | 100% (93.2 to 100.0) | 44.3% (34.2 to 54.8) | 0.50 (0.39 to 0.59) | 1.0 (0.92 to 1.0) | 1.80 (1.50 to 2.15) | 0.0 (NE) | 0.0 (0.0 to 9.2) |
| IL-1β/IL-8/ MMP-9 | 98.1% (89.9 to 100.0) | 44.3% (34.2 to 54.8) | 0.49 (0.39 to 0.60) | 0.98 (0.88 to 0.98) | 1.76 (1.47 to 2.11) | 0.04 (0.01 to 0.30) | 2.3 (1.5 to 11.9) |
| IL-1β/IL-8/MMP-8/MMP-9 | 100% (93.3 to 100.0) | 46.4% (36.2 to 56.8) | 0.51 (0.41 to 0.60) | 1.0 (0.92 to 1.0) | 1.87 (1.55 to 2.24) | 0.0 (NE) | 0.0 (0.0 to 7.8) |
| IL-1β/IL-8/MMP-8/MMP- 9/HNE | 98.1% (90.0 to 100.0) | 46.4% (36.2 to 56.8) | 0.50 (0.40 to 0.60) | 0.98 (0.89 to 0.99) | 1.83 (1.52 to 2.21) | 0.04 (0.01 to 0.29) | 2.2 (1.4 to 11.5) |
Biomarkers were log10 transformed with the addition of a constant of one before fitting into logistic regression for combinations of biomarkers. The linear predictor from each logistic regression was used to construct an ROC curve. Performance of each combination represents performance at the specific cut-point on the ROC curve.
HNE, human neutrophil elastase; IL, interleukin; −LR, negative likelihood ratio; +LR, positive likelihood ratio; MMP, matrix metalloproteinase; NE, not estimated; NPV, negative predictive value; PPV, positive predictive value; PTP, post-test probability; ROC, receiver operator characteristic.