Anatomy of an Adverse Reaction

Discussion about how to represent some of the commonest clinical concepts in an electronic health record or message has been raging for years. There has been no clear consensus. One of those tricky ones – so ubiquitous that everyone wants to have an opinion – is how to create a computable specification for an adverse reaction.

In the past few years I have been involved in much research and many discussions with colleagues around the world about how to represent an adverse reaction in a detailed clinical model. I’d like to share some of these learnings…

The latest iteration of this Adverse Reaction model has included feedback from more than 40 clinicians, informaticians and other experts from 8 countries.

Drawing from this collaborative and collective work:


An adverse reaction is “a harmful or undesirable effect associated with exposure to any substance or agent, including food, plants, animals, venom from animal stings or a medication at therapeutic or sub-therapeutic doses”.


“To record information about any adverse reaction, including:

  • immune mediated reactions Types I-IV (including allergic reactions and hypersensitivities), and
  • non-immune mediated reactions (including pseudoallergic reactions, side effects, intolerances, drug toxicities (eg Gentamycin), drug-drug interactions, food-drug interactions, drug-disease interactions and idiosyncratic reactions).”

As a result we have created one model for all types of adverse reactions, including allergic reactions, intolerances or side effects.

The scope of the model reflects the commonest use-case requirements – a pragmatic decision. It is well understood that others, including immunologists, will require much more structured data for their assessment and imputation activities. Similarly formal reporting to jurisdictions may require more structured data. Further detailed models designed for these purposes can be nested in the SLOTs that are identified in the model, below.


“Use to provide a single place within the health record to record a range of clinical statements about adverse reactions, including:

  • Record cumulative information about each exposure to a known substance, class of substance or agent; and
  • Record a clinician’s opinion that administration of, or exposure to, a substance or agent is absolutely contraindicated.”

It will record information about adverse reaction that can be both stored in the EHR and be exchanged with other systems, including as one component of a multi-faceted Adverse Reaction Report sent to statutory authorities.



Some of the things we’ve learned along the way:

  • There is a need to represent multiple reaction events per adverse reaction substance.
  • There is a need to represent a generic substance or class of substance PLUS specific substances on a per exposure basis. For example the class of penicillins AND exposure to amoxycillin and/or phenoxymethylpenicillin.
  • Severity has been very contentious. Making sense of Severity outlines some of the common issues around clinical use of severity. The specific issues about use of ‘Severity’ in the context of Adverse reaction follow:
    • In discussion with clinicians we have had a lot of pushback about attributing a consistent way of describing ‘severity’ to the ‘reaction event’, and in fact, whether it added any value at all. As a result we removed it from the model. Other qualitative descriptors have been considered including clinical impact on the patient etc but there has been no consensus. Our approach is to continue deliberations on these and add them as a part of a revision in the future if necessary.
    • More importantly, we concluded that it is a serious safety risk to attribute a ‘Severity’ to the ‘adverse reaction’ itself. What does a ‘severe adverse reaction’ actually mean? If we are trying to describe the propensity or risk of a reaction if the person is exposed to the substance or agent next time then we are attempting to predict the future a la ‘crystal ball gazing’. We cannot reasonably predict a risk of reaction being mild or moderate. A mild reaction this time does not imply a mild reaction next time and cannot preclude the potential for anaphylaxis at next exposure. Persisting this ‘guess’ in the record can potentially dangerously influence future clinical decision-making. However, conversely, some reactions observed can indicate that the next exposure are potentially catastrophic eg anaphylaxis.
      Our premise is that by adding an adverse reaction entry to an EHR the clinician is effectively flagging a relative contraindication. We have not (based on clinician feedback) included a ‘Severity’ of either the adverse reaction itself or the reaction event. We have included a flag for a clinician to mark only as true if they regard that there is an absolute contraindication (ie unacceptable risk for deliberate future exposure) for that substance/agent.
  • ‘Manifestation’ has been included specifically to allow recording of ‘the clinical manifestation of the adverse reaction expressed as a single word, phrase or brief description, e.g. nausea or rash’.
  • Based on some UK NHS CUI guidelines, it would seem reasonable that first line information available for a clinician in a system will include the same of the substance/agent, the manifestations at each reaction event, source of information. We are suggesting adding the absolute contraindication flag. No mention of severity. Second line information will include the other information in the model, plus potential links to the specific reaction events recorded elsewhere in the record, if available.

1 thought on “Anatomy of an Adverse Reaction

  1. Pingback: ICMCC News Page » Anatomy of an Adverse Reaction

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