Nexus EMR profile for the Observation resource, based on CA-Core. Represents measurements, tests, and simple assertions originating from source EMRs for aggregation.
Elements / Details
Every element this profile touches, with its full definition. Element names in the tables link here.
Represents clinical measurements, findings, and results, capturing key details
like observation type, value, status, and effective time using standard
Nexus EMR references. Uses instance-specific identifiers for tracking
observations across systems.
Comments
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.
The metadata about the resource. This is content that is maintained by the infrastructure. Changes to the content might not always be associated with version changes to the resource.
May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
The version specific identifier, as it appears in the version portion of the URL. This value changes when the resource is created, updated, or deleted.
Comments
The server assigns this value, and ignores what the client specifies, except in the case that the server is imposing version integrity on updates/deletes.
When the resource last changed - e.g. when the version changed.
Comments
This value is always populated except when the resource is first being created. The server / resource manager sets this value; what a client provides is irrelevant. This is equivalent to the HTTP Last-Modified and SHOULD have the same value on a read interaction.
Identifies EMR instance & pipeline version the resource came from
Definition
A URI that identifies the EMR pipeline and version from which this resource originated. This tells you which EMR instance (recommend using the instance identifier), and the version of the pipeline code/transformations.
Comments
In the provenance resource, this corresponds to Provenance.entity.what[x]. The exact use of the source (and the implied Provenance.entity.role) is left to implementer discretion. Only one nominated source is allowed; for additional provenance details, a full Provenance resource should be used.
This element can be used to indicate where the current master source of a resource that has a canonical URL if the resource is no longer hosted at the canonical URL.
It is up to the server and/or other infrastructure of policy to determine whether/how these claims are verified and/or updated over time. The list of profile URLs is a set.
Security labels applied to this resource. These tags connect specific resources to the overall security policy and infrastructure.
Comments
The security labels can be updated without changing the stated version of the resource. The list of security labels is a set. Uniqueness is based the system/code, and version and display are ignored.
Tags applied to this resource. Tags are intended to be used to identify and relate resources to process and workflow, and applications are not required to consider the tags when interpreting the meaning of a resource.
Comments
The tags can be updated without changing the stated version of the resource. The list of tags is a set. Uniqueness is based the system/code, and version and display are ignored.
A set of rules under which this content was created
Definition
A reference to a set of rules that were followed when the resource was constructed, and which must be understood when processing the content. Often, this is a reference to an implementation guide that defines the special rules along with other profiles etc.
Comments
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 it's narrative along with other profiles, value sets, etc.
Cardinality
0..1
Type
uri
Modifier
yes — This element is labeled as a modifier because the implicit rules may provide additional knowledge about the resource that modifies it's meaning or interpretation
The base language in which the resource is written.
Comments
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).
A human-readable narrative summary of the NexusEmrCoreObservation resource for human interpretation.
Comments
Contained resources do not have 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.
These resources do not have an independent existence apart from the resource that contains them - they cannot be identified independently, and nor can they have their own independent transaction scope.
Comments
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.
May be used to represent additional information that is not part of the basic definition of the resource. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
Prevention/screening status (completed externally, refused, ...)
Definition
May be used to represent additional information that is not part of the basic definition of the resource. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
May be used to represent additional information that is not part of the basic definition of the resource. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
Detail accompanying a screening result (independent of value[x])
Definition
May be used to represent additional information that is not part of the basic definition of the resource. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
Instructions given to the patient for this prevention
Definition
May be used to represent additional information that is not part of the basic definition of the resource. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
May be used to represent additional information that is not part of the basic definition of the resource and that modifies the understanding of the element that contains it and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer is allowed to define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension. Applications processing a resource are required to check for modifier extensions.
Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).
Requirements
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.
Comments
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.
Cardinality
0..*
Type
Extension
Modifier
yes — Modifier extensions are expected to modify the meaning or interpretation of the resource that contains them
Unique identifiers for the observation.
A business identifier is recommended but not required (identifier is 0..*). Where available, carry the source-system identifier using the most appropriate system URI. No specific canonical system is mandated.
Requirements
Allows observations to be distinguished and referenced.
Comments
A source system's own identifier SHOULD be carried alongside this one, flagged use = secondary. See Carrying the raw code.
May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
A coded type for the identifier that can be used to determine which identifier to use for a specific purpose.
Requirements
Allows users to make use of identifiers when the identifier system is not known.
Comments
This element deals only with general categories of identifiers. It SHOULD not be used for codes that correspond 1..1 with the Identifier.system. Some identifiers may fall into multiple categories due to common usage. Where the system is known, a type is unnecessary because the type is always part of the system definition. However systems often need to handle identifiers where the system is not known. There is not a 1:1 relationship between type and system, since many different systems have the same type.
Establishes the namespace for the value - that is, a URL that describes a set values that are unique.
Requirements
There are many sets of identifiers. To perform matching of two identifiers, we need to know what set we're dealing with. The system identifies a particular set of unique identifiers.
The portion of the identifier typically relevant to the user and which is unique within the context of the system.
Comments
If the value is a full URI, then the system SHALL be urn:ietf:rfc:3986. The value's primary purpose is computational mapping. As a result, it may be normalized for comparison purposes (e.g. removing non-significant whitespace, dashes, etc.) A value formatted for human display can be conveyed using the Rendered Value extension. Identifier.value is to be treated as case sensitive unless knowledge of the Identifier.system allows the processer to be confident that non-case-sensitive processing is safe.
The Identifier.assigner may omit the .reference element and only contain a .display element reflecting the name or other textual information about the assigning organization.
A plan, proposal or order that is fulfilled in whole or in part by this event. For example, a MedicationRequest may require a patient to have laboratory test performed before it is dispensed.
Requirements
Allows tracing of authorization for the event and tracking whether proposals/recommendations were acted upon.
The status of the result value. Indicates whether the observation is complete and verified.
Requirements
Need to track the status of individual results. Some results are finalized before the whole report is finalized.
Comments
This is a modifier element. Preliminary results should be interpreted with caution.
Cardinality
1..1
Type
code
Must Support
yes
Modifier
yes — This element is labeled as a modifier because it is a status element that contains status entered-in-error which means that the resource should not be treated as valid
A code that classifies the general type of observation being made. Common categories include vital-signs, laboratory, imaging, survey, exam, therapy, and activity.
Requirements
Used for filtering what observations are retrieved and displayed.
Comments
This profile constrains category to exactly one (1..1) -- carry the observation's standard clinical category (e.g. vital-signs | laboratory | imaging | exam | social-history | survey). A prevention Observation is NOT distinguished by its category: it uses its normal clinical category and is marked as a prevention by a coding under the nexus-emr-prevention-catalog NamingSystem on Observation.code.coding.
Type of observation (e.g., vital sign, laboratory test, imaging observation).
REQUIRED: text element for human readability
RECOMMENDED: LOINC code when available
OPTIONAL: Raw EMR observation codes for source system preservation
Nexus EMR does not mandate a specific coding system for observations.
The text element ensures human readability even when coded values are not recognized.
Where this code was mapped from a source system's own vocabulary, carry the raw coding alongside the mapped one, flagged userSelected = true. See Carrying the raw code.
Requirements
Knowing what kind of observation is being made is essential to understanding the observation.
Comments
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.
May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
A reference to a code defined by a terminology system.
Requirements
Allows for alternative encodings within a code system, and translations to other code systems.
Comments
Codes may be defined very casually in enumerations, or code lists, up to very formal definitions such as SNOMED CT - see the HL7 v3 Core Principles for more information. Ordering of codings is undefined and SHALL NOT be used to infer meaning. Generally, at most only one of the coding values will be labeled as UserSelected = true.
LOINC code for the observation type when available
Requirements
Allows for alternative encodings within a code system, and translations to other code systems.
Comments
Codes may be defined very casually in enumerations, or code lists, up to very formal definitions such as SNOMED CT - see the HL7 v3 Core Principles for more information. Ordering of codings is undefined and SHALL NOT be used to infer meaning. Generally, at most only one of the coding values will be labeled as UserSelected = true.
May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
The identification of the code system that defines the meaning of the symbol in the code.
Requirements
Need to be unambiguous about the source of the definition of the symbol.
Comments
The URI may be an OID (urn:oid:...) or a UUID (urn:uuid:...). OIDs and UUIDs SHALL be references to the HL7 OID registry. Otherwise, the URI should come from HL7's list of FHIR defined special URIs or it should reference to some definition that establishes the system clearly and unambiguously.
The version of the code system which was used when choosing this code. Note that a well-maintained code system does not need the version reported, because the meaning of codes is consistent across versions. However this cannot consistently be assured, and when the meaning is not guaranteed to be consistent, the version SHOULD be exchanged.
Comments
Where the terminology does not clearly define what string should be used to identify code system versions, the recommendation is to use the date (expressed in FHIR date format) on which that version was officially published as the version date.
A symbol in syntax defined by the system. The symbol may be a predefined code or an expression in a syntax defined by the coding system (e.g. post-coordination).
Indicates that this coding was chosen by a user directly - e.g. off a pick list of available items (codes or displays).
Requirements
This has been identified as a clinical safety criterium - that this exact system/code pair was chosen explicitly, rather than inferred by the system based on some rules or language processing.
Comments
Amongst a set of alternatives, a directly chosen code is the most appropriate starting point for new translations. There is some ambiguity about what exactly 'directly chosen' implies, and trading partner agreement may be needed to clarify the use of this element and its consequences more completely.
Plain text representation of the observation type, required for all entries
Requirements
The codes from the terminologies do not always capture the correct meaning with all the nuances of the human using them, or sometimes there is no appropriate code at all. In these cases, the text is used to capture the full meaning of the source.
Comments
Very often the text is the same as a displayName of one of the codings.
What the observation is about, when it is not about the subject of record
Definition
The actual focus of an observation when it is not the patient of record representing something or someone associated with the patient such as a spouse, parent, fetus, or donor. For example, fetus observations in a mother's record. The focus of an observation could also be an existing condition, an intervention, the subject's diet, another observation of the subject, or a body structure such as tumor or implanted device. An example use case would be using the Observation resource to capture whether the mother is trained to change her child's tracheostomy tube. In this example, the child is the patient of record and the mother is the focus.
Comments
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 focusCode.
The date and time this version of the observation was made available to providers, typically after the results have been reviewed and verified.
Comments
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.
Who performed the observation; repeat for an outside performer
Definition
Who was responsible for the observation.
A performer this system holds a record for is referenced normally, with reference and a display
carrying the readable name. A performer it does NOT hold a record for -- a clinician at an outside
clinic who performed a screening reported back to us -- is a display-only reference: display
carries the name as recorded and reference is absent. That is base R4's own shape for naming a
party with nothing to resolve, and it is the shape to use rather than any encoding inside free text.
The element repeats, so a record may name both: the provider here who owns the entry, and the
outside provider who performed it. A consumer distinguishes them by whether reference is present,
never by position.
Requirements
May give a degree of confidence in the observation and also indicates where follow-up questions should be directed.
Comments
Where an Observation records a prevention performed outside this clinic, the outside performer named here is the companion to a prevention status of completed-externally; the status says it happened elsewhere and this says who. Neither is derived from the other, and either may be present alone.
Provides a reason why the expected value in the element Observation.value[x] is missing.
Requirements
For many results it is necessary to handle exceptional values in measurements.
Comments
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.
Clinical comments on the observation -- one whole comment per repeat
Definition
Free-text clinical comment about this observation: what a person wanted to say about it that no
other element carries.
One whole comment per repeat.note.text is the comment in full, and a consumer renders it
verbatim.
note.text is not a carrier for other fields. A consumer MUST NOT parse it for prefixes,
markers, keys or any other in-band convention, and a producer MUST NOT encode in it a value that
belongs to an element or an extension of its own. Anything with its own editing lifecycle -- one
box, edited and cleared on its own -- gets its own address. On this resource the worked examples are
the prevention result detail
and the prevention instructions,
both of which are extensions for exactly this reason.
Requirements
Need to be able to provide free text additional information.
Comments
Attribution is OPTIONAL here, unlike on a task. author[x] and time keep their base R4 cardinality: a producer that has them SHOULD write them, a consumer displays them when present, and no consumer may require them -- comments reaching this element from a source system routinely carry neither. This is why the element is a plain Annotation rather than the Task Note profile, which requires both because a task's turns must each say who said it. Where both are absent, the comment is attributable only to the resource's own provenance.
Indicates the site on the subject's body where the observation was made (i.e. the target site).
Comments
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.
If the use case requires BodySite to be handled as a separate resource (e.g. to identify and track separately) then use the standard extension bodySite.
The specimen that was used when this observation was made.
Comments
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).
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.
Provides guide for interpretation of the observation value. May include age, gender, or other factors.
Requirements
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.
Comments
Reference ranges help determine if values are normal or abnormal for the specific patient.
May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
Extensions that cannot be ignored even if unrecognized
Definition
May be used to represent additional information that is not part of the basic definition of the element and that modifies the understanding of the element in which it is contained and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension. Applications processing a resource are required to check for modifier extensions.
Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).
Requirements
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.
Comments
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.
Cardinality
0..*
Type
Extension
Modifier
yes — Modifier extensions are expected to modify the meaning or interpretation of the element that contains them
The value of the low bound of the reference range. The low bound of the reference range endpoint is inclusive of the value (e.g. reference range is >=5 - <=9). If the low bound is omitted, it is assumed to be meaningless (e.g. reference range is <=2.3).
The value of the high bound of the reference range. The high bound of the reference range endpoint is inclusive of the value (e.g. reference range is >=5 - <=9). If the high bound is omitted, it is assumed to be meaningless (e.g. reference range is >= 2.3).
Codes to indicate the target population this reference range applies to. For example, a reference range may be based on the normal population or a particular sex or race. Multiple appliesTo are interpreted as an "AND" of the target populations. For example, to represent a target population of African American females, both a code of female and a code for African American would be used.
Requirements
Need to be able to identify the target population for proper interpretation.
Comments
This SHOULD be populated if there is more than one range. If this element is not present then the normal population is assumed.
Text based reference range in an observation which may be used when a quantitative range is not appropriate for an observation. An example would be a reference value of "Negative" or a list or table of "normals".
Related resource that belongs to the Observation group
Definition
This observation is a group observation (e.g. a battery, a panel of tests, a set of vital sign measurements) that includes the target as a member of the group.
Comments
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.
The target resource that represents a measurement from which this observation value is derived. For example, a calculated anion gap or a fetal measurement based on an ultrasound image.
Comments
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.
Used when an observation has multiple component observations. For example, blood pressure has systolic and diastolic components.
Requirements
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.
Comments
Each component observation stands alone but is interpreted in the context of the overall observation.
May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.
Comments
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.
Extensions that cannot be ignored even if unrecognized
Definition
May be used to represent additional information that is not part of the basic definition of the element and that modifies the understanding of the element in which it is contained and/or the understanding of the containing element's descendants. Usually modifier elements provide negation or qualification. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension. Applications processing a resource are required to check for modifier extensions.
Modifier extensions SHALL NOT change the meaning of any elements on Resource or DomainResource (including cannot change the meaning of modifierExtension itself).
Requirements
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.
Comments
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.
Cardinality
0..*
Type
Extension
Modifier
yes — Modifier extensions are expected to modify the meaning or interpretation of the element that contains them
The information determined as a result of making the observation, if the information has a simple value.
Requirements
An observation exists to have a value, though it might not if it is in error, or if it represents a group of observations.
Comments
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 Observation.code. A 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 Observation.code defines a coded value. For additional guidance, see the Notes section below.
Cardinality
0..1
Type
Quantity, CodeableConcept, string, boolean, integer, Range, Ratio, SampledData, time, dateTime, Period
Provides a reason why the expected value in the element Observation.component.value[x] is missing.
Requirements
For many results it is necessary to handle exceptional values in measurements.
Comments
"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.
A categorical assessment of an observation value. For example, high, low, normal.
Requirements
For some results, particularly numeric results, an interpretation is necessary to fully understand the significance of a result.
Comments
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.
Provides guide for interpretation of component result
Definition
Guidance on how to interpret the value by comparison to a normal or recommended range.
Requirements
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.
Comments
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.