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Saturday, February 27, 2016

Just the facts Ma'am

We like to think we store facts in our EHR systems. It’s just not that simple. Sometimes even the experts disagree.  The following is derived from a recent response I made on the HL7 Patient Care list on allergies.

An Allergy Observation A that states “no known allergies” at a particular point in time can certainly coexist with an Allergy Observation B that indicates an allergy to nuts that occurred at a later point in time.

The Allergy Observation of B is NOT necessarily a refutation of Allergy Observation A. B may be an allergy developed later in life that did not exist at the time A was evaluated.  Those two facts are completely consistent.

The Allergy List at time A may include an observation for no known allergies.
The Allergy List at time B should include any allergies observations listed and not subsequently refuted, and so should not include “no known allergies”.

That is to say, within an Allergy List, the positive and negative assertions, and assertions of “no known allergies” found in the list should be internally consistent, but it may not be for perfectly understandable reasons.  The process of reconciliation can help here.

Some systems promote internal consistency (a best practice), while others may not, or simply cannot (see below). We all live in a world of both, and there are cases where conflicting information is useful to be aware of.

Nearly a true story...
Somewhere in some EHR, someone has recorded Allergic to Penicillin in my daughter’s allergy list. In some other EHR that have Allergic to Amoxicillin. In a third, she has Allergic to Beta Lactam Antibiotics. In a fourth it records: Allergic to Amoxicillin and NOT Allergic to Penicillin. A healthcare provider looking at an aggregated view of this data would correctly conclude that my daughter has an allergy to some antibiotic, and that further questioning is needed to understand the true case, and to Reconcile the differences. That cannot be automated, and in fact, if the provider with “Allergic to Penicillin” and the other one with “Allergic to Amoxicillin” and “NOT Allergic to Penicillin” merged, how should they reconcile the conflicts in their combined data?

So, if we want to make rules or promote best practices, I’d say finally:

Allergy Observations are independent assessments of allergies to a specific substance, class of substances, or an indication that no allergies are known.
An Allergy List is an aggregation of allergy observations.
A Reconciled Allergy List is usually an internally consistent (according to some provider’s judgment) list of allergy observations describing the patient’s current allergy status, but may include conflicting data when that information may not be able to be interpreted without more investigation.


  1. As a patient, the maintenance and accessibility of this data is important to me as I am allergic to both penicillin and sulfa drugs.

  2. Hi Keith,

    In the joint collaboration on Adverse reaction risk between openEHR and FHIR, the resulting archetype & resource reflect the positive presence of an allergy or intolerance or other adverse reactions - It is only one archetype within a family of models to express the requirements for data about adverse reactions. The other two models express positively that there is an exclusion of an adverse reaction - - or that there is no known information about an adverse reaction - - for example if the patient is unconscious.
    These three models ensure that each possibility is recordable unambiguously and ensures that negation is not reduced to a simple boolean of present/absent which can be the basis for some serious clinical safety risks.

    My understanding is that Grahame's intent was to follow a similar pattern, however given that there seem not to be these equivalent models at this point, I cannot be sure.