Observation BG

Used for simple observations such as device measurements, laboratory atomic results, vital signs, height, weight, smoking status, comments, etc. Other resources are used to provide context for observations such as laboratory reports, etc.

• dom-2: If the resource is contained in another resource, it SHALL NOT contain nested Resources
  contained.contained.empty()
• dom-3: If the resource is contained in another resource, it SHALL be referred to from elsewhere in the resource or SHALL refer to the containing resource
  contained.where((('#'+id in (%resource.descendants().reference | %resource.descendants().ofType(canonical) | %resource.descendants().ofType(uri) | %resource.descendants().ofType(url))) or descendants().where(reference = '#').exists() or descendants().where(ofType(canonical) = '#').exists() or descendants().where(ofType(canonical) = '#').exists()).not()).trace('unmatched', id).empty()
• dom-4: If a resource is contained in another resource, it SHALL NOT have a meta.versionId or a meta.lastUpdated
  contained.meta.versionId.empty() and contained.meta.lastUpdated.empty()
• dom-5: If a resource is contained in another resource, it SHALL NOT have a security label
  contained.meta.security.empty()
• dom-6: A resource should have narrative for robust management
  text.`div`.exists()
• obs-6: dataAbsentReason SHALL only be present if Observation.value[x] is not present
  dataAbsentReason.empty() or value.empty()
• obs-7: If Observation.component.code is the same as Observation.code, then Observation.value SHALL NOT be present (the Observation.component.value[x] holds the value).
  value.empty() or component.code.where(coding.intersect(%resource.code.coding).exists()).empty()
• obs-8: bodyStructure SHALL only be present if Observation.bodySite is not present
  bodySite.exists() implies bodyStructure.empty()

• rim: Entity, Role, or Act,Observation[classCode=OBS, moodCode=EVN]
• workflow: Event
• w5: clinical.diagnostics
• sct-concept: < 363787002 |Observable entity|
• v2: OBX

Within the context of the FHIR RESTful interactions, the resource has an id except for cases like the create and conditional update. Otherwise, the use of the resouce id depends on the given use case.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

Asserting this rule set restricts the content to be only understood by a limited set of trading partners. This inherently limits the usefulness of the data in the long term. However, the existing health eco-system is highly fractured, and not yet ready to define, collect, and exchange data in a generally computable sense. Wherever possible, implementers and/or specification writers should avoid using this element. Often, when used, the URL is a reference to an implementation guide that defines these special rules as part of its narrative along with other profiles, value sets, etc.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

Language is provided to support indexing and accessibility (typically, services such as text to speech use the language tag). The html language tag in the narrative applies to the narrative. The language tag on the resource may be used to specify the language of other presentations generated from the data in the resource. Not all the content has to be in the base language. The Resource.language should not be assumed to apply to the narrative automatically. If a language is specified, it should it also be specified on the div element in the html (see rules in HTML5 for information about the relationship between xml:lang and the html lang attribute).

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

Contained resources do not have a narrative. Resources that are not contained SHOULD have a narrative. In some cases, a resource may only have text with little or no additional discrete data (as long as all minOccurs=1 elements are satisfied). This may be necessary for data from legacy systems where information is captured as a "text blob" or where text is additionally entered raw or narrated and encoded information is added later.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• rim: Act.text?

This should never be done when the content can be identified properly, as once identification is lost, it is extremely difficult (and context dependent) to restore it again. Contained resources may have profiles and tags in their meta elements, but SHALL NOT have security labels.

• rim: N/A

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• ext-1: Must have either extensions or value[x], not both
  extension.exists() != value.exists()

• rim: N/A

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• ext-1: Must have either extensions or value[x], not both
  extension.exists() != value.exists()

• rim: N/A

Allows observations to be distinguished and referenced.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• workflow: Event.identifier
• w5: FiveWs.identifier
• v2: OBX-21 For OBX segments from systems without OBX-21 support a combination of ORC/OBR and OBX must be negotiated between trading partners to uniquely identify the OBX segment. Depending on how V2 has been implemented each of these may be an option: 1) OBR-3 + OBX-3 + OBX-4 or 2) OBR-3 + OBR-4 + OBX-3 + OBX-4 or 3) some other way to uniquely ID the OBR/ORC + OBX-3 + OBX-4.
• rim: id

ObservationDefinition can be referenced by its canonical url using instantiatesCanonical, or by a name or an identifier using the appropriate sub-elements of instantiatesReference.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• workflow: Event.instantiatesCanonical
• rim: .outboundRelationship[typeCode=DEFN].target

Allows tracing of authorization for the event and tracking whether proposals/recommendations were acted upon.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• workflow: Event.basedOn
• v2: ORC
• rim: .inboundRelationship[typeCode=COMP].source[moodCode=EVN]

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: ORC
• rim: .inboundRelationship[typeCode=COMP].source[moodCode=EVN]

• rim: n/a

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• ext-1: Must have either extensions or value[x], not both
  extension.exists() != value.exists()

• rim: n/a

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• ext-1: Must have either extensions or value[x], not both
  extension.exists() != value.exists()

• rim: N/A

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• rim: outBoundRelationship

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• rim: code

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• rim: annotation

To link an Observation to an Encounter use encounter. See the Notes below for guidance on referencing another Observation.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• workflow: Event.partOf
• v2: Varies by domain
• rim: .outboundRelationship[typeCode=FLFS].target

Need to track the status of individual results. Some results are finalized before the whole report is finalized.

This element is labeled as a modifier because the status contains codes that mark the resource as not currently valid.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• workflow: Event.status
• w5: FiveWs.status
• sct-concept: < 445584004 |Report by finality status|
• v2: OBX-11
• rim: status Amended & Final are differentiated by whether it is the subject of a ControlAct event with a type of "revise"

Used for filtering what observations are retrieved and displayed.

In addition to the required category valueset, this element allows various categorization schemes based on the owner’s definition of the category and effectively multiple categories can be used at once. The level of granularity is defined by the category concepts in the value set.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• w5: FiveWs.class
• rim: .outboundRelationship[typeCode="COMP].target[classCode="LIST", moodCode="EVN"].code

Knowing what kind of observation is being made is essential to understanding the observation.

All code-value and, if present, component.code-component.value pairs need to be taken into account to correctly understand the meaning of the observation.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

{
  "coding": [
    {
      "system": "http://loinc.org",
      "code": "32016-8"
    }
  ]
}

• workflow: Event.code
• w5: FiveWs.what[x]
• sct-concept: < 363787002 |Observable entity| OR < 386053000 |Evaluation procedure|
• v2: OBX-3
• rim: code
• sct-attr: 116680003 |Is a|

Observations have no value if you don't know who or what they're about.

One would expect this element to be a cardinality of 1..1. The only circumstance in which the subject can be missing is when the observation is made by a device that does not know the patient. In this case, the observation SHALL be matched to a patient through some context/channel matching technique, and at this point, the observation should be updated. The subject of an Observation may in some cases be a procedure. This supports the regulatory inspection use case where observations are captured during inspections of a procedure that is being performed (independent of any particular patient or whether patient related at all).

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• workflow: Event.subject
• w5: FiveWs.subject[x]
• v2: PID-3
• rim: participation[typeCode=RTGT]

Typically, an observation is made about the subject - a patient, or group of patients, location, or device - and the distinction between the subject and what is directly measured for an observation is specified in the observation code itself ( e.g., "Blood Glucose") and does not need to be represented separately using this element. Use specimen if a reference to a specimen is required. If a code is required instead of a resource use either bodysite for bodysites or the standard extension http://hl7.org/fhir/StructureDefinition/observation-focusCode.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• w5: FiveWs.subject[x]
• v2: OBX-3
• rim: participation[typeCode=SBJ]

For some observations it may be important to know the link between an observation and a particular encounter.

This will typically be the encounter the event occurred within, but some events may be initiated prior to or after the official completion of an encounter but still be tied to the context of the encounter (e.g. pre-admission laboratory tests).

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• workflow: Event.encounter
• w5: FiveWs.context
• v2: PV1
• rim: inboundRelationship[typeCode=COMP].source[classCode=ENC, moodCode=EVN]

Knowing when an observation was deemed true is important to its relevance as well as determining trends.

At least a date should be present unless this observation is a historical report. For recording imprecise or "fuzzy" times (For example, a blood glucose measurement taken "after breakfast") use the Timing datatype which allow the measurement to be tied to regular life events.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• workflow: Event.occurrence[x]
• w5: FiveWs.done[x]
• v2: OBX-14, and/or OBX-19 after v2.4 (depends on who observation made)
• rim: effectiveTime

For Observations that don't require review and verification, it may be the same as the lastUpdated time of the resource itself. For Observations that do require review and verification for certain updates, it might not be the same as the lastUpdated time of the resource itself due to a non-clinically significant update that doesn't require the new version to be reviewed and verified again.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• w5: FiveWs.recorded
• v2: OBR-22 (or MSH-7), or perhaps OBX-19 (depends on who observation made)
• rim: participation[typeCode=AUT].time

May give a degree of confidence in the observation and also indicates where follow-up questions should be directed.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• workflow: Event.performer.actor
• w5: FiveWs.actor
• v2: OBX-15 / (Practitioner) OBX-16, PRT-5:PRT-4='RO' / (Device) OBX-18 , PRT-10:PRT-4='EQUIP' / (Organization) OBX-23, PRT-8:PRT-4='PO'
• rim: participation[typeCode=PRF]

An observation exists to have a value, though it might not if it is in error, or if it represents a group of observations.

• An observation may have:
  1. a single value here
  2. both a value and a set of related or component values
  3. only a set of related or component values.
• If a value is present, the datatype for this element should be determined by the code.
• CodeableConcept with just a text would be used instead of a string if the field was usually coded, or if the type associated with the code defines a coded value.
• Attachment is used if the observation result value is a binary file such as an image. If the observation result value is derived from the binary file (for example 'X' detected and here is the the proof in this image), the binary file may be directly represented using DocumentReference and referenced by derivedFrom.
• The usage of valueReference is restricted to the MolecularSequence resource when used as a definitional resource, not as a patient-specific finding. .
• For additional guidance, see the Notes section below.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• sct-concept: < 441742003 |Evaluation finding|
• v2: OBX-2, OBX-5, OBX-6
• rim: value
• sct-attr: 363714003 |Interprets|

For many results it is necessary to handle exceptional values in measurements.

Null or exceptional values can be represented two ways in FHIR Observations. One way is to simply include them in the value set and represent the exceptions in the value. For example, measurement values for a serology test could be "detected", "not detected", "inconclusive", or "specimen unsatisfactory".

The alternate way is to use the value element for actual observations and use the explicit dataAbsentReason element to record exceptional values. For example, the dataAbsentReason code "error" could be used when the measurement was not completed. Note that an observation may only be reported if there are values to report. For example differential cell counts values may be reported only when > 0. Because of these options, use-case agreements are required to interpret general observations for null or exceptional values.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: N/A
• rim: value.nullFlavor

For some results, particularly numeric results, an interpretation is necessary to fully understand the significance of a result.

Historically used for laboratory results (known as 'abnormal flag' ), its use extends to other use cases where coded interpretations are relevant. Often reported as one or more simple compact codes this element is often placed adjacent to the result value in reports and flow sheets to signal the meaning/normalcy status of the result.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• sct-concept: < 260245000 |Findings values|
• v2: OBX-8
• rim: interpretationCode
• sct-attr: 363713009 |Has interpretation|

Need to be able to provide free text additional information.

May include general statements about the observation, or statements about significant, unexpected or unreliable results values, or information about its source when relevant to its interpretation.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: NTE-3 (partner NTE to OBX, or sometimes another (child?) OBX)
• rim: subjectOf.observationEvent[code="annotation"].value

Only used if not implicit in code found in Observation.code. In many systems, this may be represented as a related observation instead of an inline component.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• sct-concept: < 123037004 |Body structure|
• v2: OBX-20
• rim: targetSiteCode
• sct-attr: 718497002 |Inherent location|

Only used if not implicit in code found in Observation.code or bodySite is used. In many systems, this may be represented as a related observation instead of an inline component.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• rim: targetSiteCode

In some cases, method can impact results and is thus used for determining whether results can be compared or determining significance of results.

Only used if not implicit in code for Observation.code.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: OBX-17
• rim: methodCode

Should only be used if not implicit in code found in Observation.code. Observations are not made on specimens themselves; they are made on a subject, but in many cases by the means of a specimen. Note that although specimens are often involved, they are not always tracked and reported explicitly. Also note that observation resources may be used in contexts that track the specimen explicitly (e.g. Diagnostic Report).

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• obs-9: If Observation.specimen is a reference to Group, the group can only have specimens
  (reference.resolve().exists() and reference.resolve() is Group) implies reference.resolve().member.entity.resolve().all($this is Specimen)

• sct-concept: < 123038009 |Specimen|
• v2: SPM segment
• rim: participation[typeCode=SPC].specimen
• sct-attr: 704319004 |Inherent in|

Note that this is not meant to represent a device involved in the transmission of the result, e.g., a gateway. Such devices may be documented using the Provenance resource where relevant.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• sct-concept: < 49062001 |Device|
• v2: OBX-17 / PRT -10
• rim: participation[typeCode=DEV]
• sct-attr: 424226004 |Using device|

Knowing what values are considered "normal" can help evaluate the significance of a particular result. Need to be able to provide multiple reference ranges for different contexts.

Most observations only have one generic reference range. 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.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• obs-3: Must have at least a low or a high or text
  low.exists() or high.exists() or text.exists()

• v2: OBX-7
• rim: outboundRelationship[typeCode=REFV]/target[classCode=OBS, moodCode=EVN]

• rim: n/a

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• ext-1: Must have either extensions or value[x], not both
  extension.exists() != value.exists()

• rim: n/a

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• ext-1: Must have either extensions or value[x], not both
  extension.exists() != value.exists()

• rim: N/A

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: OBX-7
• rim: value:IVL_PQ.low

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: OBX-7
• rim: value:IVL_PQ.high

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: OBX-7
• rim: value:IVL_PQ.normal

Need to be able to say what kind of reference range this is - normal, recommended, therapeutic, etc., - for proper interpretation.

This SHOULD be populated if there is more than one range. If this element is not present then the normal range is assumed.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• sct-concept: < 260245000 |Findings values| OR < 365860008 |General clinical state finding| OR < 250171008 |Clinical history or observation findings| OR < 415229000 |Racial group| OR < 365400002 |Finding of puberty stage| OR < 443938003 |Procedure carried out on subject|
• v2: OBX-10
• rim: interpretationCode

Need to be able to identify the target population for proper interpretation.

This SHOULD be populated if there is more than one range. If this element is not present then the normal population is assumed.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• sct-concept: < 260245000 |Findings values| OR < 365860008 |General clinical state finding| OR < 250171008 |Clinical history or observation findings| OR < 415229000 |Racial group| OR < 365400002 |Finding of puberty stage| OR < 443938003 |Procedure carried out on subject|
• v2: OBX-10
• rim: interpretationCode

Some analytes vary greatly over age.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• rim: outboundRelationship[typeCode=PRCN].targetObservationCriterion[code="age"].value

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: OBX-7
• rim: value:ST

When using this element, an observation will typically have either a value or a set of related resources, although both may be present in some cases. For a discussion on the ways Observations can assembled in groups together, see Notes below. Note that a system may calculate results from QuestionnaireResponse into a final score and represent the score as an Observation.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: Relationships established by OBX-4 usage
• rim: outBoundRelationship

All the reference choices that are listed in this element can represent clinical observations and other measurements that may be the source for a derived value. The most common reference will be another Observation. For a discussion on the ways Observations can assembled in groups together, see Notes below.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: Relationships established by OBX-4 usage
• rim: .targetObservation

Component observations share the same attributes in the Observation resource as the primary observation and are always treated a part of a single observation (they are not separable). However, the reference range for the primary observation value is not inherited by the component values and is required when appropriate for each component observation.

For a discussion on the ways Observations can be assembled in groups together see Notes below.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: containment by OBX-4?
• rim: outBoundRelationship[typeCode=COMP]

• rim: n/a

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• ext-1: Must have either extensions or value[x], not both
  extension.exists() != value.exists()

• rim: n/a

Modifier extensions allow for extensions that cannot be safely ignored to be clearly distinguished from the vast majority of extensions which can be safely ignored. This promotes interoperability by eliminating the need for implementers to prohibit the presence of extensions. For further information, see the definition of modifier extensions.

There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())
• ext-1: Must have either extensions or value[x], not both
  extension.exists() != value.exists()

• rim: N/A

Knowing what kind of observation is being made is essential to understanding the observation.

All code-value and component.code-component.value pairs need to be taken into account to correctly understand the meaning of the observation.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• w5: FiveWs.what[x]
• sct-concept: < 363787002 |Observable entity| OR < 386053000 |Evaluation procedure|
• v2: OBX-3
• rim: code

An observation exists to have a value, though it might not if it is in error, or if it represents a group of observations.

Used when observation has a set of component observations:

• An observation may have both a value (e.g. an Apgar score) and component observations (the observations from which the Apgar score was derived).
• If a value is present, the datatype for this element should be determined by the code.
• CodeableConcept with just a text would be used instead of a string if the field was usually coded, or if the type associated with the code defines a coded value.
• Attachment is used if the observation result value is a binary file such as an image. If the observation result value is derived from the binary file (for example 'X' detected and here is the the proof in this image), the binary file may be directly represented using DocumentReference and referenced by derivedFrom.
• If a value is present, the datatype for this element should be determined by the code.
• CodeableConcept with just a text would be used instead of a string if the field was usually coded, or if the type associated with the code defines a coded value.
• Attachment is used if the observation result value is a binary file such as an image. If the observation result value is derived from the binary file (for example 'X' detected and here is the the proof in this image), the binary file may be directly represented using DocumentReference and referenced by derivedFrom.
• The usage of valueReference is restricted to the MolecularSequence resource when used as a definitional resource, not as a patient-specific finding. .
• For additional guidance, see the Notes section below.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• sct-concept: 363714003 |Interprets| < 441742003 |Evaluation finding|
• v2: OBX-2, OBX-5, OBX-6
• rim: value
• sct-attr: 363714003 |Interprets|

For many results it is necessary to handle exceptional values in measurements.

"Null" or exceptional values can be represented two ways in FHIR Observations. One way is to simply include them in the value set and represent the exceptions in the value. For example, measurement values for a serology test could be "detected", "not detected", "inconclusive", or "test not done".

The alternate way is to use the value element for actual observations and use the explicit dataAbsentReason element to record exceptional values. For example, the dataAbsentReason code "error" could be used when the measurement was not completed. Because of these options, use-case agreements are required to interpret general observations for exceptional values.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: N/A
• rim: value.nullFlavor

For some results, particularly numeric results, an interpretation is necessary to fully understand the significance of a result.

Historically used for laboratory results (known as 'abnormal flag' ), its use extends to other use cases where coded interpretations are relevant. Often reported as one or more simple compact codes this element is often placed adjacent to the result value in reports and flow sheets to signal the meaning/normalcy status of the result.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• sct-concept: < 260245000 |Findings values|
• v2: OBX-8
• rim: interpretationCode
• sct-attr: 363713009 |Has interpretation|

Knowing what values are considered "normal" can help evaluate the significance of a particular result. Need to be able to provide multiple reference ranges for different contexts.

Most observations only have one generic reference range. 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.

• ele-1: All FHIR elements must have a @value or children
  hasValue() or (children().count() > id.count())

• v2: OBX-7
• rim: outboundRelationship[typeCode=REFV]/target[classCode=OBS, moodCode=EVN]