Fourteen diagnostic cohort studies were included in the review (n=3,981 participants). Study quality was modest. No studies received an A rating. One study was rated B. Six studies were rated C. Seven studies were rated D. Ten studies reported using consecutive enrolment.
C reactive protein (five studies): The pooled positive likelihood ratio was 3.15 (95% CI 2.67 to 3.71; five studies) and the pooled negative likelihood ratio was 0.33 (95% CI 0.22 to 0.49; five studies) across all cut-off values.
White blood cell count (seven studies): White blood cell indicators were less valuable than inflammatory markers for ruling in serious infection. The positive likelihood ratio ranged from 0.87 to 2.43. The negative likelihood ratio ranged from 0.61 to 1.14, which indicated no value for ruling out serious infection.
Band count (three studies): The positive likelihood ratio ranged from 1.45 to 3.05 and the negative likelihood ratio ranged from 0.65 to 0.97.
Procalcitonin (three studies): The positive likelihood ratio ranged from 1.75 to 3.11 and the negative likelihood ratio ranged from 0.08 to 0.35.
Interleukins (two studies): The positive likelihood ratio ranged from 1.89 to 2.74 and the negative likelihood ratio ranged from 0.33 to 0.77.
Absolute neutrophil count (two studies): The positive likelihood ratio ranged from 1.06 to 1.38 and the negative likelihood ratio ranged from 0.90 to 0.93.
The best performing clinical decision rule was testing urinalysis in combination with C reactive protein and procalcitonin, with a positive likelihood ratio of 4.92 (95% CI 3.26 to 7.43) and a negative likelihood ratio of 0.07 (95% CI 0.02 to 0.27).
Summary ROC curves showed that the shape of curves for C reactive protein and procalcitonin were generally similar and the confidence intervals largely overlapped, which indicated comparable diagnostic accuracy. Most data points for white blood cell count lay close to the centre of the plot, which indicated limited diagnostic value
Only one included study assessed left shift test or erythrocyte sedimentation rate. Further results were reported.