<?xml version="1.0" encoding="UTF-8"?><CodeSystem xmlns="http://hl7.org/fhir"><id value="reaction-event-severity"/><meta><lastUpdated value="2026-03-31T17:43:31.836+00:00"/></meta><text><status value="generated"/><div xmlns="http://www.w3.org/1999/xhtml"><p class="res-header-id"><b>Generated Narrative: CodeSystem reaction-event-severity</b></p><a name="reaction-event-severity"> </a><a name="hcreaction-event-severity"> </a><p>This case-sensitive code system <code>http://hl7.org/fhir/reaction-event-severity</code> defines the following codes:</p><table class="codes"><tr><td style="white-space:nowrap"><b>Code</b></td><td><b>Display</b></td><td><b>Definition</b></td></tr><tr><td style="white-space:nowrap">mild<a name="reaction-event-severity-mild"> </a></td><td>Mild</td><td>Causes mild physiological effects.</td></tr><tr><td style="white-space:nowrap">moderate<a name="reaction-event-severity-moderate"> </a></td><td>Moderate</td><td>Causes moderate physiological effects.</td></tr><tr><td style="white-space:nowrap">severe<a name="reaction-event-severity-severe"> </a></td><td>Severe</td><td>Causes severe physiological effects.</td></tr></table></div></text><extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-wg"><valueCode value="pc"/></extension><extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-standards-status"><valueCode value="normative"/></extension><extension url="http://hl7.org/fhir/StructureDefinition/structuredefinition-fmm"><valueInteger value="3"/></extension><url value="http://hl7.org/fhir/reaction-event-severity"/><identifier><system value="urn:ietf:rfc:3986"/><value value="urn:oid:2.16.840.1.113883.4.642.4.136"/></identifier><identifier><use value="old"/><system value="urn:ietf:rfc:3986"/><value value="urn:oid:2.16.840.1.113883.4.642.1.126"/></identifier><identifier><use value="old"/><system value="urn:ietf:rfc:3986"/><value value="urn:oid:2.16.840.1.113883.4.642.2.56"/></identifier><version value="6.0.0-ballot4"/><name value="AllergyIntoleranceSeverity"/><title value="Allergy Intolerance Severity"/><status value="active"/><experimental value="false"/><date value="2021-01-05T10:01:24+11:00"/><publisher value="HL7 (FHIR Project)"/><contact><telecom><system value="url"/><value value="http://hl7.org/fhir"/></telecom><telecom><system value="email"/><value value="fhir@lists.hl7.org"/></telecom></contact><description value="Clinical assessment of the severity of a reaction event as a whole, potentially considering multiple different manifestations."/><jurisdiction><coding><system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/><code value="001"/><display value="World"/></coding></jurisdiction><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/reaction-event-severity"/><content value="complete"/><concept><code value="mild"/><display value="Mild"/><definition value="Causes mild physiological effects."/></concept><concept><code value="moderate"/><display value="Moderate"/><definition value="Causes moderate physiological effects."/></concept><concept><code value="severe"/><display value="Severe"/><definition value="Causes severe physiological effects."/></concept></CodeSystem>