As two of the developers of the recently updated National Institute for Health and Care Excellence (NICE) guideline on feverish illness in children,1 we welcome the paper by De and colleagues2 In their study, the authors investigated the potential of using the white blood count (WBC) as a screening tool in the triage of children with feverish illness.

Paediatricians and other clinicians have struggled for years to find ways of identifying the handful of children with serious illnesses among the thousands who present with fever. It has often been the case that accurate histories, careful examination and clinical acumen are not enough and children with serious illnesses are missed while others with self-limiting viral illnesses are unnecessarily admitted to hospital. In an attempt to reliably identify children with serious illness, we are tempted to use a range of investigations. These include urinalysis, chest X-rays, acute phase reactants and the WBC. During the production of the NICE feverish illness guideline, we performed systematic reviews on all of these investigations. We found that the utility of the WBC has been investigated on numerous occasions in the past and the results have been extremely variable. Most of the studies found were of low quality but in those judged to be of reasonable quality estimates of the sensitivity for detecting serious illness ranged from 20% to 76%. Specificity ranged from 58% to 100%. We concluded that we had insufficient evidence to make general recommendations about the utility of WBC. However, we did identify two specific situations in which cut-offs for WBC could be useful. The first was in feverish children aged 2–3 months who appeared outwardly well. In this situation, a WBC>15×10⁹/L or <5×10⁹/L could identify a child requiring further investigation.3 The other was in the child with …