Current guidelines for using computed tomography (CT) in patients with head injury should be applied cautiously in patients who present to the emergency department (ED) more than 24 hours post-injury, new findings suggest.

“This is a group of patients in which such guidelines were not derived and validated,” Dr. Carl Marincowitz of Hull Royal Infirmary in Hull, UK, told Reuters Health by email. “The study that we have completed shows that although predictive of injuries, the sole use of such guidelines in patients presenting after 24 hours of injury would lead to significant injuries not being identified.”

Five percent of patients who present to the ED with head injury are admitted to the hospital, while 1% require neurosurgical intervention, the researchers noted in an article online in Emergency Medicine Journal.

Clinical decision rules aim to distinguish between patients with mild to minor head injuries who can be discharged based on clinical history and examination, and those who require CT scanning to rule out significant pathology. However, the researchers added, the widely used Canadian CT Head Rule was derived from and validated in patients who presented within 24 hours of injury. It has been unclear whether patients who present later are at higher or lower risk of significant injury.

To investigate, the researchers reviewed CT scans for 650 adult head trauma patients, including 101 (15.5%) who presented after 24 hours. Nearly 9% of the CT scans showed significant traumatic abnormality, and the percentage was similar for patients presenting within and after 24 hours. The likelihood of requiring neurosurgery was 0.9% for the patients presenting within 24 hours and 3% for those presenting later, although this was not a statistically significant difference. There was no guideline indication for CT scanning in 13.7% of those presenting within 24 hours of injury and 38.6% of those presenting after that period, however.

In patients who presented within 24 hours, the sensitivity of the guidelines for identifying an indication for CT scan was 97.8% in patients with traumatic intracranial findings and 100% in patients with neurosurgical outcomes or death. But the sensitivity fell to 70% and 75%, respectively, for patients presenting later.

The findings suggest, the investigators stated, that patients presenting after 24 hours for head trauma are not a lower-risk group.

Guidelines should acknowledge which populations they are, and are not, applicable to, Dr. Marincowitz told Reuters Health. “Any head injury guidelines based upon the Canadian CT head rule should acknowledge that patients presenting after 24 hours of injury should be treated cautiously until further research about this group has been conducted to assess which risk factors predict significant injuries in this group,” the researcher said.