<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019eb58b-b1c1-75c0-88ab-0c4b7f3b985d,g:7546e44d-56af-4222-af0b-dc2e5a627edd-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:dgx="http://questdiagnostics.com/20260618" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2024-01-31" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://questdiagnostics.com/20260618">
  <xs:import namespace="http://fasb.org/srt/2026" schemaLocation="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd"/>
  <xs:import namespace="http://fasb.org/us-gaap-ebp/2026" schemaLocation="https://xbrl.fasb.org/us-gaap/2026/ebp/elts/us-gaap-ebp-2026.xsd"/>
  <xs:import namespace="http://fasb.org/us-gaap/2026" schemaLocation="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2024-01-31" schemaLocation="https://www.xbrl.org/dtr/type/2024-01-31/types.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei/2026" schemaLocation="https://xbrl.sec.gov/dei/2026/dei-2026.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="dgx-20260618_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="dgx-20260618_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="dgx-20260618_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="dgx-20260618_cal.xml" xlink:role="http://www.xbrl.org/2003/role/calculationLinkbaseRef" xlink:type="simple"/>
      <link:roleType id="Cover" roleURI="http://questdiagnostics.com/role/Cover">
        <link:definition>0000001 - Document - Cover</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StatementsofNetAssetsAvailableforBenefits" roleURI="http://questdiagnostics.com/role/StatementsofNetAssetsAvailableforBenefits">
        <link:definition>0000002 - Statement - Statements of Net Assets Available for Benefits</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="StatementofChangesinNetAssetsAvailableforBenefits" roleURI="http://questdiagnostics.com/role/StatementofChangesinNetAssetsAvailableforBenefits">
        <link:definition>0000003 - Statement - Statement of Changes in Net Assets Available for Benefits</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DescriptionofthePlan" roleURI="http://questdiagnostics.com/role/DescriptionofthePlan">
        <link:definition>0000004 - Disclosure - Description of the Plan</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPolicies" roleURI="http://questdiagnostics.com/role/SummaryofSignificantAccountingPolicies">
        <link:definition>0000005 - Disclosure - Summary of Significant Accounting Policies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurements" roleURI="http://questdiagnostics.com/role/FairValueMeasurements">
        <link:definition>0000006 - Disclosure - Fair Value Measurements</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingencies" roleURI="http://questdiagnostics.com/role/CommitmentsandContingencies">
        <link:definition>0000007 - Disclosure - Commitments and Contingencies</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ScheduleHLine4iScheduleofAssetsHeldatEndofYear" roleURI="http://questdiagnostics.com/role/ScheduleHLine4iScheduleofAssetsHeldatEndofYear">
        <link:definition>0000008 - Disclosure - Schedule H, Line 4i &#8211; Schedule of Assets (Held at End of Year)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="SummaryofSignificantAccountingPoliciesPolicies" roleURI="http://questdiagnostics.com/role/SummaryofSignificantAccountingPoliciesPolicies">
        <link:definition>0000009 - Disclosure - Summary of Significant Accounting Policies (Policies)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsTables" roleURI="http://questdiagnostics.com/role/FairValueMeasurementsTables">
        <link:definition>0000010 - Disclosure - Fair Value Measurements (Tables)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="DescriptionofthePlanDetails" roleURI="http://questdiagnostics.com/role/DescriptionofthePlanDetails">
        <link:definition>0000011 - Disclosure - Description of the Plan (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="FairValueMeasurementsDetails" roleURI="http://questdiagnostics.com/role/FairValueMeasurementsDetails">
        <link:definition>0000012 - Disclosure - Fair Value Measurements (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="CommitmentsandContingenciesDetails" roleURI="http://questdiagnostics.com/role/CommitmentsandContingenciesDetails">
        <link:definition>0000013 - Disclosure - Commitments and Contingencies (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ScheduleHLine4iScheduleofAssetsHeldatEndofYearDetails" roleURI="http://questdiagnostics.com/role/ScheduleHLine4iScheduleofAssetsHeldatEndofYearDetails">
        <link:definition>0000014 - Disclosure - Schedule H, Line 4i &#8211; Schedule of Assets (Held at End of Year) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType id="ScheduleHLine4iScheduleofAssetsHeldatEndofYearDetails_1" roleURI="http://questdiagnostics.com/role/ScheduleHLine4iScheduleofAssetsHeldatEndofYearDetails_1">
        <link:definition>0000014 - Disclosure - Schedule H, Line 4i &#8211; Schedule of Assets (Held at End of Year) (Details)</link:definition>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="dgx_EBP333Member" abstract="true" name="EBP333Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="dgx_EBPParticipantContributionPretaxMinimumAnnualCompensationToTotalCompensationPercentage" abstract="false" name="EBPParticipantContributionPretaxMinimumAnnualCompensationToTotalCompensationPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="dgx_EBPRequisiteServicePeriod" abstract="false" name="EBPRequisiteServicePeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="dgx_EBPParticipantContributionMaximumContributionToInvestmentPercentage" abstract="false" name="EBPParticipantContributionMaximumContributionToInvestmentPercentage" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="dgx_EBPParticipateContributionMaximumBalanceOfInvestmentPercent" abstract="false" name="EBPParticipateContributionMaximumBalanceOfInvestmentPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="dgx_EBPNoteReceivableFromParticipantMaximumNumberOfLoansOutstanding" abstract="false" name="EBPNoteReceivableFromParticipantMaximumNumberOfLoansOutstanding" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="dgx_EBPNoteReceivableFromParticipantGeneralLoanMaximumBorrowingTerm" abstract="false" name="EBPNoteReceivableFromParticipantGeneralLoanMaximumBorrowingTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="dgx_EBPNoteReceivableFromParticipantAccountPrimaryResidenceMaximumBorrowingTerm" abstract="false" name="EBPNoteReceivableFromParticipantAccountPrimaryResidenceMaximumBorrowingTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="dgx_EBPNoteReceivableFromParticipantPercentOfVestedAccountBalanceToSecureLoans" abstract="false" name="EBPNoteReceivableFromParticipantPercentOfVestedAccountBalanceToSecureLoans" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="dgx_EBPParticipantLoanBasisSpreadOnVariableRate" abstract="false" name="EBPParticipantLoanBasisSpreadOnVariableRate" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="dgx_EBPNumberOfPutativeClassActionLawsuits" abstract="false" name="EBPNumberOfPutativeClassActionLawsuits" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
</xs:schema>
