The year 2019 marks the 10th anniversary of the publication of the Pediatric Emergency Care Applied Research Network clinical decision instrument for the identification of children at very low risk of clinically important traumatic brain injury (PECARN TBI).1 It is the largest, but hardly the only, entrant in the field. The United Kingdom contributes the children’s head injury algorithm for the prediction of important clinical events (CHALICE), and Canada contributes the Canadian assessment of tomography for childhood head injury (CATCH).2,3
These instruments arose from recognition of the increasing use of computed tomography (CT) in children as well as harms from radiation often exceeding the risks from missed injuries. These decision instruments, PECARN TBI in particular, have been widely promoted and used since their introduction.
The question remains, however, are they really necessary? As previously discussed, decision instruments are rarely validated against usual practice.4 More frequently, the best comparison for their performance comes from the derivation cohort. Looking at the original studies, the added value of these decision instruments remains a matter of reasonable question. The derivation of CHALICE is anachronistic enough to not be relevant, with a 3 percent rate of CT and a 23 percent rate of skull X-ray. In PECARN TBI, the base rate for imaging is 35 percent; in CATCH, 53 percent. In these contexts, it is less impressive that PECARN TBI classifies only 53 to 58 percent of the population as very low risk, while CATCH performs similarly, excluding just 48 percent.
Almost by serendipity, illumination arrives from below the equator in the form of a large comparative study of the three decision instruments.5 The authors of this study state, “In some countries, such as Australia and New Zealand, no clinical decision rules predominate.” And the purpose of their study is most reasonably framed by the question, which of these instruments ought we generally disseminate and encourage in our practice? The answer, according to their headliner analysis published in The Lancet, is any of them.
Direct, head-to-head comparisons are difficult because each instrument is tested in a slightly different population. For example, PECARN TBI contains specific language regarding the exclusion of trivial mechanisms of injury. CATCH has its own specific inclusion criteria limiting its application, while CHALICE was derived from a population without exclusions and can be applied to any child with a minor head injury. In their study, with slightly more than 20,000 children, the instruments all performed similarly, separated only by narrow differences. The most sensitive instrument was PECARN TBI, followed by CATCH and then CHALICE, but injuries were so rare that the 95 percent confidence intervals all overlap. Logically, the negative predictive value of each tool was between 99.7 and 100 percent. Comparing specificity and inferring the number of children in whom a CT would be performed are difficult because PECARN TBI creates an explicit observation or CT cohort, but effectively, the balance between sensitivity and specificity is as expected—one waxes as the other wanes.