<status value="active"/><experimental value="false"/><date value="2021-04-15T12:25:09+10:00"/><description value="Used to specify why the normally expected content of the data element is missing."/><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/data-absent-reason"/><content value="complete"/><concept><code value="unknown"/><display value="Unknown"/><definition value="The value is expected to exist but is not known."/><concept><code value="asked-unknown"/><display value="Asked But Unknown"/><definition value="The source was asked but does not know the value."/></concept><concept><code value="temp-unknown"/><display value="Temporarily Unknown"/><definition value="There is reason to expect (from the workflow) that the value may become known."/></concept><concept><code value="not-asked"/><display value="Not Asked"/><definition value="The workflow didn't lead to this value being known."/></concept><concept><code value="asked-declined"/><display value="Asked But Declined"/><definition value="The source was asked but declined to answer."/></concept></concept><concept><extension url="http://hl7.org/fhir/StructureDefinition/codesystem-concept-comments"><valueString value="Using "masked" may be breach of security or confidentiality, but there are times when its use is required to support alternate workflows for gaining access to denied information."/></extension><code value="masked"/><display value="Masked"/><definition value="The information is not available due to security, privacy or related reasons."/></concept><concept><code value="not-applicable"/><display value="Not Applicable"/><definition value="There is no proper value for this element (e.g. last menstrual period for a male)."/></concept><concept><code value="unsupported"/><display value="Unsupported"/><definition value="The source system wasn't capable of supporting this element."/></concept><concept><extension url="http://hl7.org/fhir/StructureDefinition/codesystem-concept-comments"><valueString value="It may be linked by internal references (e.g. xml:id). This usually implies that the value could not be represented in the correct format - this may be due to system limitations, or this particular data value."/></extension><code value="as-text"/><display value="As Text"/><definition value="The content of the data is represented in the resource narrative."/></concept><concept><code value="error"/><display value="Error"/><definition value="Some system or workflow process error means that the information is not available."/><concept><extension url="http://hl7.org/fhir/StructureDefinition/codesystem-concept-comments"><valueString value="This is sometimes an output value from measuring devices."/></extension><code value="not-a-number"/><display value="Not a Number (NaN)"/><definition value="The numeric value is undefined or unrepresentable due to a floating point processing error."/></concept><concept><extension url="http://hl7.org/fhir/StructureDefinition/codesystem-concept-comments"><valueString value="This is sometimes an output value from measuring devices."/></extension><code value="negative-infinity"/><display value="Negative Infinity (NINF)"/><definition value="The numeric value is excessively low and unrepresentable due to a floating point processing error."/></concept><concept><extension url="http://hl7.org/fhir/StructureDefinition/codesystem-concept-comments"><valueString value="This is sometimes an output value from measuring devices."/></extension><code value="positive-infinity"/><display value="Positive Infinity (PINF)"/><definition value="The numeric value is excessively high and unrepresentable due to a floating point processing error."/></concept></concept><concept><code value="not-performed"/><display value="Not Performed"/><definition value="The value is not available because the observation procedure (test, etc.) was not performed."/></concept><concept><extension url="http://hl7.org/fhir/StructureDefinition/codesystem-concept-comments"><valueString value="This is most often associated with required bindings that do not include the actual code used, but may be used with other data types."/></extension><code value="not-permitted"/><display value="Not Permitted"/><definition value="The value is not permitted in this context (e.g. due to profiles, or the base data types)."/></concept></CodeSystem>

This code system http://terminology.hl7.org/CodeSystem/data-absent-reason defines the following codes:

Lvl	Code	Display	Definition	Comments
1	unknown	Unknown	The value is expected to exist but is not known.
2	asked-unknown	Asked But Unknown	The source was asked but does not know the value.
2	temp-unknown	Temporarily Unknown	There is reason to expect (from the workflow) that the value may become known.
2	not-asked	Not Asked	The workflow didn't lead to this value being known.
2	asked-declined	Asked But Declined	The source was asked but declined to answer.
1	masked	Masked	The information is not available due to security, privacy or related reasons.	Using "masked" may be breach of security or confidentiality, but there are times when its use is required to support alternate workflows for gaining access to denied information.
1	not-applicable	Not Applicable	There is no proper value for this element (e.g. last menstrual period for a male).
1	unsupported	Unsupported	The source system wasn't capable of supporting this element.
1	as-text	As Text	The content of the data is represented in the resource narrative.	It may be linked by internal references (e.g. xml:id). This usually implies that the value could not be represented in the correct format - this may be due to system limitations, or this particular data value.
1	error	Error	Some system or workflow process error means that the information is not available.
2	not-a-number	Not a Number (NaN)	The numeric value is undefined or unrepresentable due to a floating point processing error.	This is sometimes an output value from measuring devices.
2	negative-infinity	Negative Infinity (NINF)	The numeric value is excessively low and unrepresentable due to a floating point processing error.	This is sometimes an output value from measuring devices.
2	positive-infinity	Positive Infinity (PINF)	The numeric value is excessively high and unrepresentable due to a floating point processing error.	This is sometimes an output value from measuring devices.
1	not-performed	Not Performed	The value is not available because the observation procedure (test, etc.) was not performed.
1	not-permitted	Not Permitted	The value is not permitted in this context (e.g. due to profiles, or the base data types).	This is most often associated with required bindings that do not include the actual code used, but may be used with other data types.