Extending AllergyIntolerance.reaction.severity?


Looking for a good recommendation on how to indicate a “Fatal” severity.

Background: We currently collect allergy severity that is closer to the C-CDA specs which includes Fatal. There’s a concern is we try to do a mapping of “Fatal” to “Severe” that we would lose the significant risk this value has with the patient.

From what I understand reading the specs –
• Severity has a Required binding – can only be Mild | Moderate | Severe
• Because of the Required binding, expanding on this value set would be frowned upon

The only thing I can think of doing would to –

• Utilize a Note or Description field to indicate this Severity, or
• Add some sort of “extension” within the reaction element

My first preference would be to extend the severity value set that would closer match the C-CDA specs; which includes 6 values.

Patrick Peyton


Does Fatal indicate that the patient has already passed away? If not, how is fatal usefully different to a severe allergy? Does severe mean something other than life threatening?

Irrespective of that, the expectation is that you can put an extension on the severity that carries your internal severity code as well as having severe as the code


That’s for the reply Grahamegrieve. Sorry to be delayed on my reply.

From what I understand, severe could be something like difficult breathing - assistance is needed. Where Fatal could cause actual death. I’m sure this item has been discussed back and forth before.

Does anyone know why severity doesn’t closely match the Consolidated CDA standards? There are six (6) items defined there.


Difficulty breathing generally has the potential to be fatal. There was a great deal of clinical discussion over a period of about a year to land on the current set. The CCDA value set was an input to those discussions.


I question whether we are talking about AllergyIntolerance.reaction.severity OR AllergyIntolerance.criticality. Based on the earlier comment

Fatal could cause actual death

The resource supports a distinction between potential risk (what could happen) versus actual account of a past reaction (what did happen). If you want to represent the potential risk of death, then I would recommend using AllergyIntolerance.criticality

The FHIR specification has some guidance as follows:

  • Criticality is the worst it could be in the future (i.e. situation-agnostic) whereas severity is situation-dependent.
  • Existing systems that are capturing both condition criticality and reaction severity may use the term “severity” to represent both

AllergyIntolerance.criticality of high risk = Worst case result of a future exposure is assessed to be life-threatening or having high potential for organ system failure.