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Observation, Condition, Diagnosis, Concern

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3.4

NOTE: The HL7 Patient Care Technical Committee is developing a formal model for condition tracking. The examples provided here are greatly simplified so as to illustrate certain aspects of SNOMED CT implementation.


Observations, Conditions, Diagnoses, and Concerns are often confused, but in fact have distinct definitions and patterns.


  • "Observation" and "Condition": An HL7 observation is something noted and recorded as an isolated event, whereas an HL7 condition is an ongoing event. Symptoms and findings (also know as signs) are observations. The distinction between "seizure" and "epilepsy" or between "allergic reaction" and "allergy" is that the former is an observation, and the latter is a condition.


SNOMED CT distinguishes between "Clinical Findings" and "Diseases", where a SNOMED CT disease is a kind of SNOMED CT clinical finding that is necessarily abnormal:

    • [ 404684003 | Clinical finding ]
      • [ 64572001 | Disease ]

The SNOMED CT finding/disease distinction is orthogonal to the HL7 observation/condition distinction, thus a SNOMED CT finding or disease can be an HL7 observation or condition.

  • "Diagnosis": The term "diagnosis" has many clinical and administrative meanings in healthcare
    • A diagnosis is the result of a cognitive process whereby signs, symptoms, test results, and other relevant data are evaluated to determine the condition afflicting a patient.
    • A diagnosis often directs administrative and clinical workflow, where for instance the assertion of an admission diagnosis establishes care paths, order sets, etc.
    • A diagnosis is often something that is billed for in a clinical encounter. In such a scenario, an application typically has a defined context where the billable object gets entered.


  • "Concern": A concern is something that a clinician is particularly interested in and wants to track. It has important patient management use cases (e.g. health records often present the problem list or list of concerns as a way of summarizing a patient's medical history).

Differentiation of Observation, Condition, Diagnosis, and Concern in common patterns:


  • "Observation" and "Condition": The distinction between an HL7 Observation and HL7 Condition is made by setting the Act.classCode to "OBS" or "COND", respectively. The distinction between a SNOMED finding and SNOMED disease is based on the location of the concept in the SNOMED CT hierarchy. There is no flag in a clinical statement instance for distinguishing between a SNOMED CT finding vs. disease.


  • "Diagnosis":
    • Result of a cognitive process: Could potentially be Indicated by post-coordinating a SNOMED CT finding method attribute with a procedure such as "cognitive process".
    • Directs administrative and clinical workflow: These use cases typically rely more on the context in which the diagnoses are entered (e.g. where an order set has a field designated for the admission diagnosis). In such a case, the distinction of a (particular kind of) diagnosis is that it occurs within a particular organizer (e.g. a condition within an Admission Diagnosis section is an admission diagnosis from an administrative perspective).
      • Something that is billed for: The fact that something was billed for would be expressed in another HL7 message. There is nothing in the pattern for a diagnosis that says whether or not it was or can be billed for.


  • "Concern": The HL7 Patient Care Technical Committee is developing a formal model for condition tracking. In that model, a problem (which may be an Observation, a Procedure, or some other type of Act) is wrapped in an Act with a new Act.classCode “CONCERN”. The focus in this guide is on the use of SNOMED CT, whereas the Patient Care condition tracking model is the definitive source for the overall structure of a problem list.

It should be noted that the administrative representation of a diagnosis and the representation of a concern break the rules from section ‎3.1.1 Observations vs. Organizers, in that these designations are based on context, whereas the designation of something as an Observation vs. Condition is inherent in the clinical statement itself.


3.4.1
<observation classCode="OBS" moodCode="EVN">
  <code code="ASSERTION" codeSystem="2.16.840.1.113883.5.4"/>
  <text>Headache</text>
  <value xsi:type="CD" code="25064002|Headache|" codeSystem="2.16.840.1.113883.6.96">
    <displayName value="Headache"/>
  </value>
</observation>

The observation is asserting a clinical finding of "headache".


3.4.2
<act classCode="DOCSECT" moodCode="EVN">
  <code code="8646-2" codeSystem="2.16.840.1.113883.6.1" codeSystemName="LOINC"/>
  <title>Hospital Admission Diagnosis</title>
  <text>Hospital admission diagnosis of headache</text>
  <actRelationship typeCode="COMP">
    <observation classCode="OBS" moodCode="EVN">
      <code code="ASSERTION" codeSystem="2.16.840.1.113883.5.4"/>
      <value xsi:type="CD" code="25064002|Headache|" codeSystem="2.16.840.1.113883.6.96">
        <displayName="Headache"/>
      </value>
    </observation>
  </actRelationship>
</act>

That a given diagnosis is, for instance, an Admission Diagnosis, can be asserted by wrapping the observation within a particular organizer.


3.4.3
<act classCode="DOCSECT" moodCode="EVN">
  <code code="11450-4" codeSystem="2.16.840.1.113883.6.1" codeSystemName="LOINC"/>
  <title>Problem List</title>
  <text>
    <list>
      <item>Headache</item>
      <item>Osteoarthritis of knee</item>
    </list>
  </text>
  <actRelationship typeCode="COMP">  
    <act classCode="CONCERN" moodCode="EVN">
      <actRelationship typeCode="SUBJ">
        <observation classCode="OBS" moodCode="EVN">
          <code code="ASSERTION" codeSystem="2.16.840.1.113883.5.4"/>
          <value xsi:type="CD" code="25064002|Headache|" codeSystem="2.16.840.1.113883.6.96">
            <displayName value="Headache"/>
          </value>
        </observation> 
      </actRelationship>
    </act>
  </actRelationship>
  <actRelationship typeCode="COMP"> 
    <act classCode="CONCERN" moodCode="EVN">
      <actRelationship typeCode="SUBJ">
        <observation classCode="OBS" moodCode="EVN">
          <code code="ASSERTION" codeSystem="2.16.840.1.113883.5.4"/>
          <value xsi:type="CD" code="239873007|Osteoarthritis of knee|" codeSystem="2.16.840.1.113883.6.96">
            <displayName value="Osteoarthritis of knee"/>
          </value>
        </observation>
      </actRelationship>
    </act>
  </actRelationship>
</act>

That a given clinical statement is a part of a condition tracking structure can be asserted by containing the clinical statement within the concern act, using the mechanism defined by the HL7 Patient Care Technical Committee, as shown here.