You need a high sensitivity to be sure that your negative result indeed predicts a true negative. That means if your clinical decision tool suggests that you don't need to get a head CT, then your head CT would have been normal.
On the flip side, this realistically means there is a low-moderate specificity. That means a clinical decision tool with at least 1 positive criterion does not always mean that there will be an abnormal finding on head CT.
There are 3 major clinical decision rules that I've heard tossed around in the literature:
- Canadian CT Head Rules (CCHR)
- New Orleans Criteria (NOC)
- National Emergency X-Radiography Utilization Study (NEXUS)-II
Take a look at these decision rules and their inclusion criteria.
- The CCHR included patients with GCS 13-15. The NOC initially enrolled only patients with a GCS of 15.
- All factor in age (≥65 years for CCHR and NEXUS-II; ≥60 years for NOC).
- Interestingly only the CCHR, for better or worse, take into account mechanism of injury. I'm not sure I would obtain a head CT on a pedestrian with a graze wound on the foot from a slow-moving vehicle.