Multilevel likelihood ratios and post-test SBI probability for each surrogate marker and clinical evaluation at different cut-off values
| Marker and cut-off | Pretest probability (%) | LR+ (95% CI) | Post-test probability if test positive (%) | LR− (95% CI) | Post-test probability if test negative (%) |
|---|---|---|---|---|---|
| PCT >0.2 ng/ml | 16 | 2.8 (2.3 to 3.2) | 35 | 0.2 (0.1 to 0.4) | 4 |
| PCT >0.5 ng/ml | 16 | 3.9 (2.6 to 5.5) | 42 | 0.5 (0.4 to 0.7) | 9 |
| PCT >2 ng/ml | 16 | 7.1 (3.4 to 14.9) | 58 | 0.8 (0.7 to 0.9) | 13 |
| PCT >10 ng/ml | 16 | ∞ (4.0 to ∞) | 100 | 0.9 (0.9 to 1.0) | 15 |
| CRP >10 mg/l | 16 | 2.1 (1.9 to 2.3) | 29 | 0.1 (0.03 to 0.3) | 2 |
| CRP >17.7 mg/l | 16 | 3.0 (2.6 to 3.2) | 36 | 0.1 (0.03 to 0.2) | 2 |
| CRP >40 mg/l | 16 | 4.4 (3.3 to 5.5) | 46 | 0.3 (0.2 to 0.4) | 5 |
| CRP >80 mg/l | 16 | 5.9 (3.5 to 9.9) | 53 | 0.6 (0.5 to 0.8) | 11 |
| WBC >10 000×106/l | 16 | 1.7 (1.5 to 1.9) | 25 | 0.2 (0.1 to 0.5) | 4 |
| WBC >14 100×106/l | 16 | 2.8 (2.2 to 3.2) | 35 | 0.3 (0.1 to 0.4) | 5 |
| WBC >20 000×106/l | 16 | 5.1 (3.2 to 7.9) | 49 | 0.6 (0.5 to 0.7) | 10 |
| ANC >5200×106/l | 16 | 2.2 (1.8 to 2.4) | 30 | 0.2 (0.1 to 0.4) | 4 |
| ANC >10 000×106/l | 16 | 3.6 (2.4 to 5.2) | 41 | 0.6 (0.4 to 0.7) | 10 |
| ANC >15 000×106/l | 16 | 5.6 (2.5 to 12.9) | 52 | 0.8 (0.8 to 0.9) | 14 |
| VAS >14.8% | 16 | 1.1 (0.9 to 1.3) | 17 | 0.8 (0.5 to 1.2) | 14 |
| VAS >25% | 16 | 1.5 (1.1 to 2.0) | 22 | 0.7 (0.6 to 1.0) | 13 |
| VAS >50% | 16 | 2.2 (1.1 to 4.4) | 30 | 0.9 (0.8 to 1.0) | 15 |
A pretest SBI probability of 16% (the SBI prevalence) was assumed.
LR+, positive likelihood ratio; LR-, negative likelihood ratio.
ANC, absolute neutrophil count; CRP, C reactive protein; PCT, procalcitonin; SBI, serious bacterial infection; VAS, visual analogue scale; WBC, white blood cells count.