With concerns over health-care rationing reaching near-hysterical levels, imagine this scenario in an ER in the not-too-distant future. A 4-year-old suffers minor head trauma, perhaps from falling off a swing and hitting her head on the ground. She is dazed, and although she doesn't lose consciousness her worried parents—visions of subdural hematomas and concussion dancing in their own heads—rush her to the local emergency room, expecting that the doctors there will immediately do a CT scan.

Surprise. The ER intake nurse talks to the child, who is able to say her name and explain what happened in the playground. She did not lose consciousness, her mother (who witnessed the fall) tells the nurse. The little girl is not vomiting, the ER doctor determines that there are no signs of fracture of the base of her skull, and she does not have a severe headache. Verdict: no CT scan.

In a more innocent age, the parents might have been puzzled, but accepting. What do you want to bet that, whatever happens to health-care reform (since the nation will continue to struggle with skyrocketing medical costs), in the current climate of rationing fears, they will be suspicious, even furious, believing that their child is being denied proper medical care for some nefarious economic reason? Yet the conclusion that children with head injuries do not necessarily need a CT scan—and that such scans expose them to high levels of cancer-causing radiation for no benefit—is supported by the largest study of its kind.

For the study, described in a paper in the online edition of The Lancet, scientists led by Nathan Kuppermann of the University of California, Davis, School of Medicine, analyzed the medical records of 42,000 children with head trauma. (The U.S. Centers for Disease Control and Prevention estimates that 435,000 children under 14 visit ERs every year to be evaluated for traumatic brain injury.) Of the 15,000 who got a CT scan, 376 had serious brain injuries, and 60 underwent surgery.

Comparing the outcomes of the 27,000 children who did not receive CT scans and had no adverse consequences from that omission, and the nearly 15,000 who did but did not benefit from it, the scientists came up with criteria for when a child should receive a CT scan after a head injury. For children under 2, if there is normal mental status, no scalp swelling, no significant loss of consciousness, no palpable skull fracture, and no behavioral changes (as reported by a parent), and if the injury occurred in a nonsevere way (something other than a car crash), it is safer to skip the CT scan. For a child 2 and older, Kuppermann and his team concluded, it is safe to skip the CT scan if he did not lose consciousness, is not vomiting, has no fracture of the base of the skull, and does not have a severe headache.