This profile defines how to represent Body Mass Index (BMI) observations in FHIR using a standard LOINC code and UCUM units of measure.

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 logical id of the resource, as used in the URL for the resource. Once assigned, this value never changes.

The only time that a resource does not have an id is when it is being submitted to the server using a create operation.

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.

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.

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.

The base language in which the resource is written.

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 that contains a summary of the resource and can be used to represent the content of the resource to a human. The narrative need not encode all the structured data, but is required to contain sufficient detail to make it "clinically safe" for a human to just read the narrative. Resource definitions may define what content should be represented in the narrative to ensure clinical safety.

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.

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.

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).

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.

A unique identifier assigned to this observation.

Allows observations to be distinguished and referenced.

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.

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

A larger event of which this particular Observation is a component or step. For example, an observation as part of a procedure.

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

The status of the result value.

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.

A code that classifies the general type of observation being made.

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.

• unordered
• Open
• discriminators: value:coding.code, value:coding.system

A code that classifies the general type of observation being made.

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.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

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.

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.

• unordered
• Open
• discriminators: value:url

A reference to a code defined by a terminology system.

Allows for alternative encodings within a code system, and translations to other code systems.

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.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

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.

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.

• unordered
• Open
• discriminators: value:url

The identification of the code system that defines the meaning of the symbol in the code.

Need to be unambiguous about the source of the definition of the symbol.

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.

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).

Need to refer to a particular code in the system.

A representation of the meaning of the code in the system, following the rules of the system.

Need to be able to carry a human-readable meaning of the code for readers that do not know the system.

Indicates that this coding was chosen by a user directly - e.g. off a pick list of available items (codes or displays).

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.

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.

A human language representation of the concept as seen/selected/uttered by the user who entered the data and/or which represents the intended meaning of the user.

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.

Very often the text is the same as a displayName of one of the codings.

Body Mass Index (BMI).

5. SHALL contain exactly one [1..1] code, where the @code SHOULD be selected from ValueSet HITSP Vital Sign Result Type 2.16.840.1.113883.3.88.12.80.62 DYNAMIC (CONF:7301).

additional codes that translate or map to this code are allowed. For example a more granular LOINC code or code that is used locally in a system.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

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.

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.

• unordered
• Open
• discriminators: value:url

A reference to a code defined by a terminology system.

Allows for alternative encodings within a code system, and translations to other code systems.

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.

• unordered
• Open
• discriminators: value:code, value:system

A reference to a code defined by a terminology system.

Allows for alternative encodings within a code system, and translations to other code systems.

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.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

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.

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.

• unordered
• Open
• discriminators: value:url

The identification of the code system that defines the meaning of the symbol in the code.

Need to be unambiguous about the source of the definition of the symbol.

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.

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).

Need to refer to a particular code in the system.

A representation of the meaning of the code in the system, following the rules of the system.

Need to be able to carry a human-readable meaning of the code for readers that do not know the system.

Indicates that this coding was chosen by a user directly - e.g. off a pick list of available items (codes or displays).

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.

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.

A human language representation of the concept as seen/selected/uttered by the user who entered the data and/or which represents the intended meaning of the user.

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.

Very often the text is the same as a displayName of one of the codings.

The patient, or group of patients, location, or device this observation is about and into whose record the observation is placed. If the actual focus of the observation is different from the subject (or a sample of, part, or region of the subject), the focus element or the code itself specifies the actual focus of the observation.

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 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.

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 healthcare event (e.g. a patient and healthcare provider interaction) during which this observation is made.

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).

Often just a dateTime for Vital Signs.

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.

The date and time this version of the observation was made available to providers, typically after the results have been reviewed and verified.

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 was responsible for asserting the observed value as "true".

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

Vital Signs value are recorded using the Quantity data type. For supporting observations such as Cuff size could use other datatypes such as CodeableConcept.

9. SHALL contain exactly one [1..1] value with @xsi:type="PQ" (CONF:7305).

An observation may have; 1) a single value here, 2) both a value and a set of related or component values, or 3) only a set of related or component values. 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.

• unordered
• Closed
• discriminators: type:$this

Vital Signs value are recorded using the Quantity data type. For supporting observations such as Cuff size could use other datatypes such as CodeableConcept.

9. SHALL contain exactly one [1..1] value with @xsi:type="PQ" (CONF:7305).

An observation may have; 1) a single value here, 2) both a value and a set of related or component values, or 3) only a set of related or component values. 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.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

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.

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.

• unordered
• Open
• discriminators: value:url

The value of the measured amount. The value includes an implicit precision in the presentation of the value.

Precision is handled implicitly in almost all cases of measurement.

The implicit precision in the value should always be honored. Monetary values have their own rules for handling precision (refer to standard accounting text books).

How the value should be understood and represented - whether the actual value is greater or less than the stated value due to measurement issues; e.g. if the comparator is "<" , then the real value is < stated value.

Need a framework for handling measures where the value is <5ug/L or >400mg/L due to the limitations of measuring methodology.

A human-readable form of the unit.

There are many representations for units of measure and in many contexts, particular representations are fixed and required. I.e. mcg for micrograms.

The identification of the system that provides the coded form of the unit.

Need to know the system that defines the coded form of the unit.

Coded responses from the common UCUM units for vital signs value set.

Need a computable form of the unit that is fixed across all forms. UCUM provides this for quantities, but SNOMED CT provides many units of interest.

The preferred system is UCUM, but SNOMED CT can also be used (for customary units) or ISO 4217 for currency. The context of use may additionally require a code from a particular system.

Provides a reason why the expected value in the element Observation.value[x] is missing.

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.

A categorical assessment of an observation value. For example, high, low, normal.

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.

Comments about the observation or the results.

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.

Indicates the site on the subject's body where the observation was made (i.e. the target site).

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.

Indicates the mechanism used to perform the observation.

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.

The specimen that was used when this observation was made.

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).

The device used to generate the observation data.

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.

Guidance on how to interpret the value by comparison to a normal or recommended range. Multiple reference ranges are interpreted as an "OR". In other words, to represent two distinct target populations, two referenceRange elements would be used.

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.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

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.

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 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).

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.

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 what part of the targeted reference population it applies to. For example, the normal or therapeutic range.

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.

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.

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.

The age at which this reference range is applicable. This is a neonatal age (e.g. number of weeks at term) if the meaning says so.

Some analytes vary greatly over age.

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".

Used when reporting vital signs panel components.

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.

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 reporting systolic and diastolic blood pressure.

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.

Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces.

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.

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 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).

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.

Describes what was observed. Sometimes this is called the observation "code".

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.

Vital Sign Value recorded with UCUM.

9. SHALL contain exactly one [1..1] value with @xsi:type="PQ" (CONF:7305).

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.

Provides a reason why the expected value in the element Observation.component.value[x] is missing.

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.

A categorical assessment of an observation value. For example, high, low, normal.

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.

Guidance on how to interpret the value by comparison to a normal or recommended range.

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.