Diagnostic performance of each test for discriminating bacterial infections from other conditions
| Onset of symptoms | Assay | Condition | Cut-off | Youden’s index | Sensitivity (95% CI) | Specificity (95% CI) | PPV (95% CI) | NPV (95% CI) |
|---|---|---|---|---|---|---|---|---|
| <24 hr | SAA (mg/L) | Maximum Youden’s index | >20.9 | 0.563 | 0.809 (0.717 to 0.875) | 0.754 (0.725 to 0.781) | 0.258 (0.230 to 0.288) | 0.974 (0.961 to 0.983) |
| At ~90% sensitivity | >7.0 | 0.495 | 0.883 (0.802 to 0.933) | 0.612 (0.579 to 0.643) | 0.193 (0.177 to 0.211) | 0.980 (0.966 to 0.989) | ||
| At ~90% specificity | >94.8 | 0.392 | 0.489 (0.391 to 0.589) | 0.902 (0.881 to 0.920) | 0.346 (0.284 to 0.413) | 0.944 (0.932 to 0.953) | ||
| CRP (mg/L) | Maximum Youden’s index | >5.2 | 0.558 | 0.798 (0.706 to 0.867) | 0.760 (0.731 to 0.787) | 0.260 (0.231 to 0.290) | 0.973 (0.960 to 0.982) | |
| At ~90% sensitivity | >1.1 | 0.403 | 0.894 (0.815 to 0.941) | 0.510 (0.477 to 0.542) | 0.161 (0.149 to 0.175) | 0.978 (0.962 to 0.988) | ||
| At ~90% specificity | >16.1 | 0.488 | 0.596 (0.495 to 0.689) | 0.892 (0.870 to 0.911) | 0.368 (0.312 to 0.429) | 0.954 (0.942 to 0.964) | ||
| ESR (mm/hr) | Maximum Youden’s index | >15 | 0.337 | 0.606 (0.505 to 0.699) | 0.731 (0.701 to 0.759) | 0.192 (0.163 to 0.224) | 0.946 (0.932 to 0.958) | |
| At ~90% sensitivity | >4 | 0.196 | 0.872 (0.790 to 0.925) | 0.323 (0.293 to 0.355) | 0.120 (0.111 to 0.129) | 0.960 (0.933 to 0.976) | ||
| At ~90% specificity | >25 | 0.210 | 0.330 (0.243 to 0.430) | 0.880 (0.857 to 0.900) | 0.225 (0.171 to 0.289) | 0.762 (0.647 to 0.863) | ||
| Neutrophil (×103/µL) | Maximum Youden’s index | >8.02 | 0.410 | 0.638 (0.538 to 0.728) | 0.772 (0.743 to 0.799) | 0.228 (0.196 to 0.264) | 0.953 (0.939 to 0.964) | |
| At ~90% sensitivity | >3.86 | 0.156 | 0.904 (0.828 to 0.949) | 0.251 (0.224 to 0.281) | 0.113 (0.106 to 0.121) | 0.961 (0.930 to 0.979) | ||
| At ~90% specificity | >11.55 | 0.221 | 0.309 (0.224 to 0.408) | 0.912 (0.892 to 0.929) | 0.271 (0.204 to 0.350) | 0.926 (0.916 to 0.935) | ||
| ≥24 hr | SAA (mg/L) | Maximum Youden’s index | >21.2 | 0.562 | 0.900 (0.821 to 0.946) | 0.662 (0.608 to 0.711) | 0.424 (0.384 to 0.465) | 0.960 (0.927 to 0.978) |
| At ~90% sensitivity | >21.2 | 0.562 | 0.900 (0.821 to 0.946) | 0.662 (0.608 to 0.711) | 0.424 (0.384 to 0.465) | 0.960 (0.927 to 0.978) | ||
| At ~90% specificity | >249.9 | 0.439 | 0.556 (0.453 to 0.654) | 0.883 (0.844 to 0.914) | 0.568 (0.481 to 0.652) | 0.878 (0.850 to 0.901) | ||
| CRP (mg/L) | Maximum Youden’s index | >14.8 | 0.516 | 0.778 (0.682 to 0.851) | 0.738 (0.688 to 0.783) | 0.452 (0.399 to 0.505) | 0.923 (0.890 to 0.947) | |
| At ~90% sensitivity | >3.1 | 0.432 | 0.900 (0.821 to 0.946) | 0.532 (0.478 to 0.586) | 0.348 (0.318 to 0.379) | 0.951 (0.911 to 0.973) | ||
| At ~90% specificity | >46.2 | 0.399 | 0.522 (0.420 to 0.622) | 0.877 (0.837 to 0.908) | 0.540 (0.453 to 0.625) | 0.869 (0.842 to 0.892) | ||
| ESR (mm/hr) | Maximum Youden’s index | >42 | 0.283 | 0.433 (0.336 to 0.536) | 0.849 (0.806 to 0.884) | 0.443 (0.359 to 0.530) | 0.844 (0.818 to 0.867) | |
| At ~90% sensitivity | >10 | 0.244 | 0.878 (0.794 to 0.930) | 0.366 (0.316 to 0.420) | 0.277 (0.255 to 0.300) | 0.915 (0.859 to 0.950) | ||
| At ~90% specificity | >47 | 0.250 | 0.367 (0.274 to 0.470) | 0.883 (0.844 to 0.914) | 0.465 (0.367 to 0.565) | 0.834 (0.811 to 0.856) | ||
| Neutrophil (×103/µL) | Maximum Youden’s index | >6.43 | 0.333 | 0.567 (0.464 to 0.664) | 0.766 (0.717 to 0.809) | 0.402 (0.339 to 0.467) | 0.865 (0.833 to 0.891) | |
| At ~90% sensitivity | >3.17 | 0.112 | 0.900 (0.821 to 0.946) | 0.212 (0.171 to 0.260) | 0.240 (0.224 to 0.257) | 0.885 (0.799 to 0.936) | ||
| At ~90% specificity | >8.61 | 0.297 | 0.411 (0.315 to 0.514) | 0.886 (0.847 to 0.916) | 0.500 (0.403 to 0.597) | 0.845 (0.820 to 0.866) | ||
| All | SAA (mg/L) | Maximum Youden’s index | >21.2 | 0.583 | 0.853 (0.795 to 0.897) | 0.729 (0.704 to 0.754) | 0.323 (0.299 to 0.348) | 0.970 (0.959 to 0.979) |
| At ~90% sensitivity | >8.5 | 0.522 | 0.902 (0.851 to 0.937) | 0.620 (0.592 to 0.647) | 0.264 (0.248 to 0.281) | 0.977 (0.964 to 0.985) | ||
| At ~90% specificity | >149.3 | 0.407 | 0.505 (0.434 to 0.577) | 0.901 (0.883 to 0.917) | 0.437 (0.383 to 0.492) | 0.923 (0.912 to 0.933) | ||
| CRP (mg/L) | Maximum Youden’s index | >10.9 | 0.553 | 0.739 (0.671 to 0.797) | 0.814 (0.791 to 0.835) | 0.376 (0.342 to 0.410) | 0.954 (0.942 to 0.963) | |
| At ~90% sensitivity | >2.0 | 0.469 | 0.891 (0.838 to 0.929) | 0.577 (0.549 to 0.605) | 0.242 (0.227 to 0.257) | 0.972 (0.959 to 0.982) | ||
| At ~90% specificity | >27.3 | 0.442 | 0.538 (0.466 to 0.609) | 0.904 (0.886 to 0.919) | 0.458 (0.405 to 0.513) | 0.928 (0.917 to 0.938) | ||
| ESR (mm/hr) | Maximum Youden’s index | >15 | 0.329 | 0.658 (0.586 to 0.722) | 0.672 (0.645 to 0.698) | 0.233 (0.210 to 0.257) | 0.928 (0.914 to 0.941) | |
| At ~90% sensitivity | >6 | 0.264 | 0.875 (0.819 to 0.915) | 0.389 (0.362 to 0.417) | 0.178 (0.168 to 0.189) | 0.954 (0.933 to 0.968) | ||
| At ~90% specificity | >33 | 0.244 | 0.359 (0.293 to 0.430) | 0.885 (0.866 to 0.902) | 0.320 (0.269 to 0.377) | 0.901 (0.891 to 0.911) | ||
| Neutrophil (×103/µL) | Maximum Youden’s index | >9.07 | 0.332 | 0.484 (0.413 to 0.555) | 0.849 (0.827 to 0.868) | 0.326 (0.284 to 0.371) | 0.916 (0.904 to 0.926) | |
| At ~90% sensitivity | >3.22 | 0.084 | 0.908 (0.857 to 0.942) | 0.177 (0.156 to 0.199) | 0.143 (0.137 to 0.150) | 0.927 (0.888 to 0.953) | ||
| At ~90% specificity | >10.54 | 0.253 | 0.353 (0.288 to 0.425) | 0.900 (0.882 to 0.915) | 0.348 (0.292 to 0.408) | 0.902 (0.892 to 0.911) |
Abbreviations: CI, confidence interval; PPV, positive predictive value; NPV, negative predictive value; SAA, serum amyloid A; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate.