Tiny Tips: The CATCH Rule

In Tiny Tips by Brent Thoma2 Comments

Yesterday CJEM tweeted out one of their latest article to become open-access: Review of the CATCH study: a clinical decision rule for the use of computed tomography in children with minor head injury. While I understand that they are not able to make all of their articles open-access due to financial considerations, they have made the effort to make those articles published >1 year ago freely available. This article provides an overview and discussion of the merits of the CATCH rule.


This meme will make sense eventually, I promise

The CATCH Rule

If you’re unfamiliar with this Canadian-derived decision rule, I suggest you check out the article. In its promising derivation study it was 100% sensitivity for detecting head injuries that required intervention using just 4 high-risk criteria in a population of 0-16 year old children that presented with minor head trauma in the last 24 hours. Minor head trauma was defined as an initial GCS of 13 or higher (as per treating physician) along with witnessed LOC, amnesia, disorientation, persistent vomiting or persistent irritability (age < 2yo). I think this effectively describes the population of kids that have had a good thwack to the head whose need for a CT scan is clinically ambiguous.


The rule also specified 3 medium risk criteria that were associated with brain injury seen on CT that did not require intervention. As nothing needed to be done, I would say these are of questionable significance from a patient-centered perspective. Relative to the more popular and validated PECARN rule, the CATCH rule has the advantage of being less ambiguous and stating who absolutely requires CT (PECARN tells us who absolutely does not). However, I suspect that in practice the medium risk criteria will often be used as “may need a CT” criteria.

While this rule has not been prospectively validated in the published literature, data from the validation study was presented at the CAEP conference in 2012. The powerpoint slides from this presentation are available here and the abstract is published here. Notably, the high risk criteria missed injuries requiring intervention (4 cases, sensitivity only 87%). Adding in the medium risk criteria missed 1 child with an EDH that presented again the next day meeting the high risk criteria (worsening headache). Ultimate conclusions on the validation of CATCH should wait until the study is formally published.

As with all Tiny Tips, in clinical practice you are advised to look the rules up! However, for exam purposes, I have a helpful mnemonic to remember the CATCH high and medium risk criteria. This may be of more relevance to Canadian EM residents as it is our home-grown rule.


I warned you wigs were coming…


Why the wigs?

Teresa Chan, a new BoringEM author, recent graduate of the McMaster University Royal College EM Program, and education researcher extraordinaire, was kind enough to contribute to my Tiny Tips section by offering some of the mnemonics that she used while studying for her exams. Her mnemonic for the high-risk criteria is WIGS and I figured there’d be nothing better to help me/you remember that than a picture of a mullet-baby and comb-over Chihuahua.

  • W – Worsening Headache
  • I – Irritability
  • G – GCS <15 2 hours after the injury
  • S – Suspected open/depressed skull #

The medium risk criteria can be remembered by thinking about one of the things you might see if you did a CT: a SDH.


  • S – Skull #
  • D – Dangerous mechanism (MVC, fall >3ft or 5 stairs, bike accident without helmet)
  • H – Hematoma (boggy)


The CATCH rule is a Canadian minor head injury clinical decision rule that has been prospectively derived with a validation study pending. A useful mnemonic for examination is presented above. When in practice, look it up! Check out Boring Cards for details on how to add flashcards for all of the mnemonics covered as Tiny Tips so far onto your smartphone.

For further information I would suggest a BMJ review published in 2011 comparing the CATCH, PECARN and CHALICE rules or listening to the EMPEM podcast from 2011 by Colin Parker.

A huge thank you to Teresa Chan for providing this mnemonic and peer reviewing this post. Props to CJEM for making their review open-access.

Dr. Brent Thoma is a medical educator, blogging geek, and trauma/emergency physician who works at the University of Saskatchewan College of Medicine. He founded BoringEM and is the CEO of CanadiEM.