This page is part of the FHIR Specification (v3.2.0: R4 Ballot 1). The current version which supercedes this version is 5.0.0. For a full list of available versions, see the Directory of published versions . Page versions: R5 R4B R4 R3 R2

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10.1 Resource Observation - Content

Orders and Observations Work Group

Maturity Level: 5

Normative

Compartments: Device, Encounter, Patient, Practitioner, RelatedPerson

Normative Candidate Note: This page is candidate normative content for R4 in the Observation Package. Once normative, it will lose it's Maturity Level, and breaking changes will no longer be made.

Measurements and simple assertions made about a patient, device or other subject.

This resource is referenced by AdverseEvent, CarePlan, ChargeItem, ClinicalImpression, Communication, CommunicationRequest, Condition, DeviceRequest, DeviceUseStatement, DiagnosticReport, FamilyMemberHistory, Goal, MedicationAdministration, MedicationRequest, MedicationStatement, Procedure, QuestionnaireResponse, Sequence, ServiceRequest and SupplyRequest

10.1.3 Resource Content

 

Alternate definitions: Master Definition (XML, JSON), XML Schema/Schematron + JSON Schema, ShEx (for Turtle) + see the extensions & the dependency analysis

10.1.3.1 Terminology Bindings

Path	Definition	Type	Reference
Observation.status	Codes providing the status of an observation.	Required	ObservationStatus
Observation.category	Codes for high level observation categories.	Preferred	Observation Category Codes
Observation.code Observation.component.code	Codes identifying names of simple observations.	Example	LOINC Codes
Observation.dataAbsentReason Observation.component.dataAbsentReason	Codes specifying why the result (Observation.value[x]) is missing.	Extensible	Observation Value Absent Reason
Observation.interpretation Observation.component.interpretation	Codes identifying interpretations of observations.	Extensible	Observation Interpretation Codes
Observation.bodySite	Codes describing anatomical locations. May include laterality.	Example	SNOMED CT Body Structures
Observation.method	Methods for simple observations.	Example	Observation Methods
Observation.referenceRange.type	Code for the meaning of a reference range.	Extensible	Observation Reference Range Meaning Codes
Observation.referenceRange.appliesTo	Codes identifying the population the reference range applies to.	Example	Observation Reference Range Applies To Codes

10.1.3.2 Constraints

• obs-3: On Observation.referenceRange: Must have at least a low or a high or text (expression on Observation.referenceRange: low.exists() or high.exists() or text.exists())
• obs-6: dataAbsentReason SHALL only be present if Observation.value[x] is not present (expression : dataAbsentReason.empty() or value.empty())
• obs-7: If Observation.code is the same as a Observation.component.code then the value element associated with the code SHALL NOT be present (expression : value.empty() or component.code.where( (coding.code = %resource.code.coding.code) and (coding.system = %resource.code.coding.system)).empty())

10.1.4 Notes:

At its simplest, a resource instances can consist of only a code and a value, and status flag. The relevance of other properties will vary based on the type of observation.

Profiles will be created to provide guidance on capturing certain types of simple observations. This resource focuses on the level of detail captured by most systems. However, any "simple" observation can easily be broken into numerous components and sub-components to provide additional information relevant in certain circumstances. As with other resources, extensions can be used to introduce this additional complexity.

10.1.4.1 Observation Grouping

Many observations have important relationships to other observations and need to be grouped together. These structures have been defined to do this: DiagnosticReport and DiagnosticReport.result, Observation and the elements: Observation.component, Observation.hasMember and Observation.derivedFrom. The sections below provides guidance around which structure to use. Because the idea of what to group together is often highly contextual and based upon the end user's point of view, the choice of which structure to use will be driven by jurisdiction, organizational practice and context. Profiling will normally be necessary for implementation.

10.1.4.1.1 DiagnosticReport.result

DiagnosticReport relates directly to an order (ServiceRequest). The DiagnosticReport.code names the panel and serves as the grouping element, which is traditionally referred to as a "panel" or "battery" by laboratories. The DiagnosticReport.result element references the individual observations. Several examples demonstrate observation grouping using DiagnosticReport as the grouping structure.

10.1.4.1.2 Observation.component

Observation.component is used for any supporting result that cannot reasonably be interpreted and used outside the scope of the Observation it is a component of. Components should only be used when there is only one method, one observation, one performer, one device, and one time. Some use cases for using this structure include:

1. Observations that are commonly produced and interpreted together. For example, systolic and diastolic blood pressure are represented as a single Blood pressure panel.
2. Assessment tool results that are commonly produced and interpreted together. For example, a newborn Apgar score that is a single Observation with five components.
3. Representing multiple answers to a question (relationship and boundaries between Observation and Questionnaire/QuestionnaireResponse). For example, reporting the types of alcohol consumed by a patient

On the other hand, any observations that are clinically relevant outside the context of being a component of another observation should be represented by separate Observation resources. For example a Body Mass Index (BMI) Observation should not contain components for height and weight because they are clinically relevant observations on their own and should be represented by separate Observation resources. See the Observation.related section below on how to relate independent Observations.

Note that the component.code may in some cases only be able to be understood in relation to the Observation.code (for example, see the $stats operation).

10.1.4.1.3 Observation.member of and Observation.derivedFrom

Observation.hasMember and Observation.derivedFrom and the core extensions: Observation-sequel-to and Observation-replaces are used for any supporting result that can be interpreted and used on its own and has one or more different values for method, observation, performer, device, time, and/or error conditions. Two common use cases for using this structure are:

1. For grouping related observations as a "panel"or "battery". In this case the Observation.code represents the "panel" code, typically Observation.value[x] is not present, and the set of member Observations are listed in Observation.hasMember. This structure permits nested grouping when used with DiagnosticReport (e.g. complex micro isolate and sensitivities report).
2. When linking to other Observations from which an Observation is derived. In this case both Observation.code and Observation.value[x] are present, and the linked observations are listed in Observation.derivedFrom. An example of this would be a Body Mass Index (BMI) Observation where the height and weight measurements are referenced.

10.1.4.2 Using codes in Observation

When a result value is a represented as a predefined concept using a code, valueCodeableConcept is used. This element is bound to a value set comprised of a standard nomenclature such as SNOMED CT or a source system ("local") coded result values.

10.1.4.2.1 Code Translations

Results may be coded in multiple value sets based on different code systems and these may be mapped using the ConceptMap resource and/or given as translations directly in the element as shown in the example below.

For example the LOINC 43304-5 Chlamydia trachomatis rRNA [Presence] in Unspecified specimen by Probe and target amplification method is typically associated with coded presence/absence concepts. Using the coded value for 'negative' with a standard code translation, valueCodeableConcept would be:

	"valueCodeableConcept": {
		"coding": [
			{
				"system": "http://snomed.info/sct",
				"code": "260385009",
				"display": "Negative"
			}, {
				"system": "https://acme.lab/resultcodes",
				"code": "NEG",
				"display": "Negative"
			}
		],
		"text": "Negative for Chlamydia Trachomatis rRNA"
	}

	

10.1.4.2.2 Text values for coded results:

When the data element is usually coded or the type associated with the code element defines a coded value, use valueCodeableConcept even if there is no appropriate code and only un-coded text is available. For example using text only, the valueCodeableConcept element would be:

	"valueCodeableConcept": {
		"text": "uncoded free text result"
	}

			

When a coded answer list includes a concept code for "other" and there is a free text description of the concept, the valueCodeableConcept.text element should be used to capture the full meaning of the source. In the example below, the answer code "Other" is provided in the valueCodeableConcept element and the text value supplied value in the CodeableConcept.text element.

{
	"resourceType": "Observation",
	... snip ...
	"code": {
		"coding": [
			{
				"system": "http://loinc.org",
				"code": "74076-1",
				"display": "Medication or substance involved"
			}
		]
	},
	.. snip ...
	"valueCodeableConcept": {
		"coding": [
			{
				"system": "http://loinc.org",
				"code": " LA20343-2",
				"display": "Other substance: PLEASE SPECIFY"
			}
		],
		"text": "Other: Blue pills I found under my couch"
	}
	.. snip ...
}
	   

10.1.4.2.3 Interoperability Issues using code value pairs in FHIR

A recurring issue for many observation events, regardless of the particular pattern, is determining how to populate observation.code and observation.value. While this is typically straight-forward for laboratory observations, it can get blurry for other types of observations, such as findings and disorders, family history observations, etc. This discussion focuses on the way in which the coded representation of such statements is expressed using the Observation.code and Observation.value elements.

There are two distinct facets that are central to a FHIR Observations:

• The action taken to make the finding and/or the property about which the property was observed. For example: measurement of blood hemoglobin.
• The result of the observation. For example: 14 g/dl.

Several different ways of representing the same information exist using different combinations of the Observation.code and Observation.value. Unconstrained use of the alternatives presents a major challenge for computation of semantic equivalence and for safe interpretation of observations originating from different applications and users. The following four patterns could reasonably represent the same case:

1. Observation.code represents the nature of the observation and the Observation.value a code represents the non-numeric result value. These are two distinct facets that are central to a FHIR Observations. For example:
   • code=[Examination]
   • value=[Abdomen tender]
2. Observation.code is nearly identical to 1) above, but the level of granularity is shifted from the value to code. For example:
   • code=[Abdominal examination]
   • value=[Tenderness]
3. The Observation.code is also expressed in a way that does not specify the observation action, but indicates a statement about findings reduced to a single name (or term), as in the above item. In this example, the Observation.value is present and "qualifies" the finding typically confirming or refuting it. For example::
   • code=[Abdominal tenderness]
   • value=[found/true]
4. in this example the Observation.code is expressed in a way that does not specify the observation action, but indicates a statement about findings reduced to a single name (or term). In this particular example in that context, the Observation.value is omitted. For example:
   • code=[Abdominal tenderness]
   • value element is omitted

10.1.4.2.4 Guidance:

1. Recommended rules for case 1 and 2 patterns:
   • The Observation.code is preferably a LOINC concept code.
     • If a SNOMED CT concept code is used, the expression SHOULD represent a 363787002 (Observable entity(Observable entity)) or 386053000 (Evaluation procedure(evaluation procedure))
   • For non-numeric values, the Observation.value is preferably a SNOMED CT concept code.
2. Recommended rules for case 3 pattern:
   • The Observation.code is preferably a SNOMED CT concept code where the concept is-a 404684003 (Clinical finding (finding)) , 413350009 (Finding with explicit context(finding)), or 272379006 (Event(event)).
   • The Observation.value is represented by either
     • valueBoolean
     • valueCodeableConcept preferably using:
       • SNOMED CT where concept is-a 362981000 (Qualifier value (qualifier value))
       • v2 Yes/no Indicator
       • v2 Expanded Yes/no Indicator (unfortunately is missing 'not given')
3. Recommended rules for case 4 pattern:
   • The Observation.code is preferably a SNOMED CT concept code where the concept is-a 404684003 (Clinical finding (finding)) , 413350009 (Finding with explicit context(finding)), or 272379006 (Event(event)).
   • The Observation.value is omitted. The default interpretation is the the concept (single code or expression) represented in Observation.code is present in the patient. A Observation.dataAbsentReason value of 'clinical-finding' SHOULD be used to indicate why the expected value is missing.
4. SHOULD NOT use the Assertion pattern as described in HL7 Version 3 Implementation Guide: TermInfo - Using SNOMED CT in CDA R2 Models, Release 1 . ( The code is 'ASSERTION' and the value is a SNOMED CT concept or expression )

10.1.4.3 Value[x] and Datatypes

• The element, Observation.value[x], has a variable name depending on the type as follows:
  • valueQuantity
  • valueCodeableConcept
  • valueString
  • valueBoolean
  • valueInteger
  • valueRange
  • valueRatio
  • valueSampledData
  • valueTime
  • valueDateTime
  • valuePeriod
  
  
• See above section on Using codes for result values
• The Boolean data type is rarely used for value[x] because most observations result values are never truly Boolean due to exceptional values such as "unknown", therefore they should use the CodeableConcept data type instead and select codes from http://hl7.org/fhir/ValueSet/v2-0136 (these "yes/no" concepts can be mapped to the display name "true/false" or other mutually exclusive terms that may be needed")
• The special values "E" (error), "L" (below detection limit) and "U" (above detection limit) can be used are in the SampledData data type. However when using valueQuantity in an observation for above and below detection limit values, valueQuantity should be used by stating the limit along with the comparator. In addition, when there is an error the dataAbsentReason element should be used with the appropriate value ('error' or 'NaN'). For example if the value was below the lower limit of detection of <2.0 mmol/L the valueQuantity would be:

  	"valueQuantity": {
  		"value": 2.0,
  		"comparator": "<",
  		"unit": "mmol/l",
  		"system": "http://unitsofmeasure.org",
  		"code": "mmol/L"
  	}
  

  If the value was "NaN" (i.e. an error) the valueCodeableConcept element would be absent and dataAbsentReason element would be:

  	"dataAbsentReason": {
  		"coding": [
  			{
  				"system": "http://hl7.org/fhir/data-absent-reason",
  				"code": "NaN",
  				"display": "Not a Number"
  			}
  		]
  	}
  	

• Because there are multiple types allowed for the value element, multiple value search parameters are defined. There is no standard parameter for searching values of type Ratio

10.1.4.4 Physiologically Relevant Time of the Observation

The effectiveDateTime or effectivePeriod is the time that the observation is most relevant as an observation of the subject. For a biological subject (e.g. a human patient), this is the physiologically relevant time of the observation. In the case of an observation using a specimen, this represents the start and end of the specimen collection (e.g. 24 hour Urine Sodium), but if the collection time is sufficiently short, this is reported as a point in time value (e.g. normal venipuncture). In the case of an observation obtained directly from a subject (e.g. BP, Chest X-ray), this is the start and end time of the observation process, which again, is often reported as a single point in time.

10.1.4.5 Reference Range

Most common observations will only have one generic reference range. Reference ranges may be useful for lab tests and other measures like systolic blood pressure, but will have little relevance for something like "pregnancy status". Systems MAY choose to restrict to only supplying the relevant reference range based on knowledge about the patient (e.g. specific to the patient's age, gender, weight and other factors), but this might not be possible or appropriate. Whenever more than one reference range is supplied, the differences between them SHOULD be provided in the reference range and/or age properties.

10.1.4.6 Canceled or Aborted Observations

If a measurement or test could not be completed (for example if the specimen is unsatisfactory or the provider cancelled the order), then the status value should be updated to "cancelled" and the specific details given - preferably as coded values in the dataAbsentReason or valueCodeableConcept element. Additional information may be provided in comments as well. The specimen reject example demonstrates this using a coded value for unsatisfactory specimen in dataAbsentReason.

10.1.4.7 Genetic Observations

Genetic reporting makes heavy use of the DiagnosticReport and Observation resources. A set of profiles have been defined for representing genetic results that can be found here.

The Clinical Genomics workgroup is currently exploring a couple of alternatives that are less dependent on extensions

• The Harvard (Tangram) proposal is published as a customized version of the HL7 FHIR specification and provides a set of interrelated composable profiles
• The NLM (genomics2) proposal is published as a FHIR implementation guide an approach that aligns with HL7's v2 clinical genomics implementation guide

These proposals are under active discussion within the Clinical Genomics WorkGroup . Feedback on these proposals can be provided to the workgroup by joining and posting to their list server, participating in a conference call or emailing the co-chairs.

10.1.5 Operations defined for Observation

10.1.5.1 Searching for the Last N Observations

The lastn query operation meets the common need for searching for the most recent or "last known" Observations for a subject. Examples where this query could be used:

• Fetch the last 5 temperatures for a patient to view trends
• Get the most recent lab results for patient
• Fetch the last 3 results for all vitals for a patient

See the Last N Observations Query section in the Observation resource operations page for more information and examples

10.1.5.2 Retrieving Statistics for Laboratory Observations

The stats operation performs a set of statistical calculations on a set of clinical measurements such as a blood pressure as stored on the server. This operation is focused on Observation resources with valueQuantity elements that have UCUM unit codes. Examples where this operation could be used:

• Get the average, min, max and count of a series of BP measurements for a patient
• Determine 20th or 80th percentile on a set of measurements over a time period

See the Observation Statistics section in the Observation resource operations page for more information and examples

10.1.6 Search Parameters

Search parameters for this resource. The common parameters also apply. See Searching for more information about searching in REST, messaging, and services.

Name	Type	Description	Expression	In Common
based-on	reference	Reference to the service request.	Observation.basedOn (CarePlan, MedicationRequest, NutritionOrder, DeviceRequest, ServiceRequest, ImmunizationRecommendation)
category	token	The classification of the type of observation	Observation.category
code	token	The code of the observation type	Observation.code	8 Resources
code-value-concept	composite	Code and coded value parameter pair	Observation
code-value-date	composite	Code and date/time value parameter pair	Observation
code-value-quantity	composite	Code and quantity value parameter pair	Observation
code-value-string	composite	Code and string value parameter pair	Observation
combo-code	token	The code of the observation type or component type	Observation.code | Observation.component.code
combo-code-value-concept	composite	Code and coded value parameter pair, including in components	Observation | Observation.component
combo-code-value-quantity	composite	Code and quantity value parameter pair, including in components	Observation | Observation.component
combo-data-absent-reason	token	The reason why the expected value in the element Observation.value[x] or Observation.component.value[x] is missing.	Observation.dataAbsentReason | Observation.component.dataAbsentReason
combo-value-concept	token	The value or component value of the observation, if the value is a CodeableConcept	Observation.value.as(CodeableConcept) | Observation.component.value.as(CodeableConcept)
combo-value-quantity	quantity	The value or component value of the observation, if the value is a Quantity, or a SampledData (just search on the bounds of the values in sampled data)	Observation.value.as(Quantity) | Observation.component.value.as(Quantity)
component-code	token	The component code of the observation type	Observation.component.code
component-code-value-concept	composite	Component code and component coded value parameter pair	Observation.component
component-code-value-quantity	composite	Component code and component quantity value parameter pair	Observation.component
component-data-absent-reason	token	The reason why the expected value in the element Observation.component.value[x] is missing.	Observation.component.dataAbsentReason
component-value-concept	token	The value of the component observation, if the value is a CodeableConcept	Observation.component.value.as(CodeableConcept)
component-value-quantity	quantity	The value of the component observation, if the value is a Quantity, or a SampledData (just search on the bounds of the values in sampled data)	Observation.component.value.as(Quantity)
context	reference	Healthcare event (Episode-of-care or Encounter) related to the observation	Observation.context (EpisodeOfCare, Encounter)
data-absent-reason	token	The reason why the expected value in the element Observation.value[x] is missing.	Observation.dataAbsentReason
date	date	Obtained date/time. If the obtained element is a period, a date that falls in the period	Observation.effective	17 Resources
derived-from	reference	Related measurements the observation is made from	Observation.derivedFrom (Media, Observation, ImagingStudy, Sequence, QuestionnaireResponse, DocumentReference)
device	reference	The Device that generated the observation data.	Observation.device (DeviceComponent, Device, DeviceMetric)
encounter	reference	Encounter related to the observation	Observation.context (Encounter)	12 Resources
has-member	reference	Related resource that belongs to the Observation group	Observation.hasMember (Observation, Sequence, QuestionnaireResponse)
identifier	token	The unique id for a particular observation	Observation.identifier	26 Resources
method	token	The method used for the observation	Observation.method
part-of	reference	Part of referenced event	Observation.partOf (Immunization, MedicationDispense, MedicationAdministration, Procedure, ImagingStudy, MedicationStatement)
patient	reference	The subject that the observation is about (if patient)	Observation.subject (Patient)	29 Resources
performer	reference	Who performed the observation	Observation.performer (Practitioner, Organization, CareTeam, Patient, PractitionerRole, RelatedPerson)
specimen	reference	Specimen used for this observation	Observation.specimen (Specimen)
status	token	The status of the observation	Observation.status
subject	reference	The subject that the observation is about	Observation.subject (Group, Device, Patient, Location)
value-concept	token	The value of the observation, if the value is a CodeableConcept	Observation.value.as(CodeableConcept)
value-date	date	The value of the observation, if the value is a date or period of time	Observation.value.as(dateTime) | Observation.value.as(Period)
value-quantity	quantity	The value of the observation, if the value is a Quantity, or a SampledData (just search on the bounds of the values in sampled data)	Observation.value.as(Quantity)
value-string	string	The value of the observation, if the value is a string, and also searches in CodeableConcept.text	Observation.value.as(string)