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    <link:label id="lab_dgx_FourPointSevenFivePercentSeniorNotesDue2020Member_CB473027A4E3510760E4AF31C7E8A1D6_terseLabel_en-US" xlink:label="lab_dgx_FourPointSevenFivePercentSeniorNotesDue2020Member_CB473027A4E3510760E4AF31C7E8A1D6" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">4.75% Senior Notes due January 2020 [Member]</link:label>
    <link:label id="lab_dgx_FourPointSevenFivePercentSeniorNotesDue2020Member_CB473027A4E3510760E4AF31C7E8A1D6_label_en-US" xlink:label="lab_dgx_FourPointSevenFivePercentSeniorNotesDue2020Member_CB473027A4E3510760E4AF31C7E8A1D6" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Four Point Seven Five Percent Senior Notes Due2020 [Member]</link:label>
    <link:label id="lab_dgx_FourPointSevenFivePercentSeniorNotesDue2020Member_CB473027A4E3510760E4AF31C7E8A1D6_documentation_en-US" xlink:label="lab_dgx_FourPointSevenFivePercentSeniorNotesDue2020Member_CB473027A4E3510760E4AF31C7E8A1D6" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Four Point Seven Five Percent Senior Notes Due 2020 [Member]</link:label>
    <link:loc xlink:href="dgx-20150930.xsd#dgx_FourPointSevenFivePercentSeniorNotesDue2020Member" xlink:label="loc_dgx_FourPointSevenFivePercentSeniorNotesDue2020Member_CB473027A4E3510760E4AF31C7E8A1D6" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dgx_FourPointSevenFivePercentSeniorNotesDue2020Member_CB473027A4E3510760E4AF31C7E8A1D6" xlink:to="lab_dgx_FourPointSevenFivePercentSeniorNotesDue2020Member_CB473027A4E3510760E4AF31C7E8A1D6" xlink:type="arc" />
    <link:label id="lab_dgx_TwoPointFiveZeroPercentSeniorNotesdueMarch2020Member_5C266FB7AD541AE45689AF31C7E81726_terseLabel_en-US" xlink:label="lab_dgx_TwoPointFiveZeroPercentSeniorNotesdueMarch2020Member_5C266FB7AD541AE45689AF31C7E81726" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">2.50% Senior Notes due March 2020 [Member]</link:label>
    <link:label id="lab_dgx_TwoPointFiveZeroPercentSeniorNotesdueMarch2020Member_5C266FB7AD541AE45689AF31C7E81726_label_en-US" xlink:label="lab_dgx_TwoPointFiveZeroPercentSeniorNotesdueMarch2020Member_5C266FB7AD541AE45689AF31C7E81726" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Two Point Five Zero Percent Senior Notes due March 2020 [Member]</link:label>
    <link:label id="lab_dgx_TwoPointFiveZeroPercentSeniorNotesdueMarch2020Member_5C266FB7AD541AE45689AF31C7E81726_documentation_en-US" xlink:label="lab_dgx_TwoPointFiveZeroPercentSeniorNotesdueMarch2020Member_5C266FB7AD541AE45689AF31C7E81726" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Two Point Five Zero Percent Senior Notes due March 2020 [Member]</link:label>
    <link:loc xlink:href="dgx-20150930.xsd#dgx_TwoPointFiveZeroPercentSeniorNotesdueMarch2020Member" xlink:label="loc_dgx_TwoPointFiveZeroPercentSeniorNotesdueMarch2020Member_5C266FB7AD541AE45689AF31C7E81726" xlink:type="locator" />
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    <link:label id="lab_dgx_FourPointSevenZeroPercentSeniorNotesdue2021Member_0B39909DDB25A58E402FAF31C7E8A144_documentation_en-US" xlink:label="lab_dgx_FourPointSevenZeroPercentSeniorNotesdue2021Member_0B39909DDB25A58E402FAF31C7E8A144" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Four Point Seven Zero Percent Senior Notes due 2021 [Member]</link:label>
    <link:loc xlink:href="dgx-20150930.xsd#dgx_FourPointSevenZeroPercentSeniorNotesdue2021Member" xlink:label="loc_dgx_FourPointSevenZeroPercentSeniorNotesdue2021Member_0B39909DDB25A58E402FAF31C7E8A144" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dgx_FourPointSevenZeroPercentSeniorNotesdue2021Member_0B39909DDB25A58E402FAF31C7E8A144" xlink:to="lab_dgx_FourPointSevenZeroPercentSeniorNotesdue2021Member_0B39909DDB25A58E402FAF31C7E8A144" xlink:type="arc" />
    <link:label id="lab_dgx_FourpointtwofivepercentSeniorNotesDue2024Member_8B76B43A42CEFF8BA452AF31C7E83C1C_terseLabel_en-US" xlink:label="lab_dgx_FourpointtwofivepercentSeniorNotesDue2024Member_8B76B43A42CEFF8BA452AF31C7E83C1C" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">4.25% Senior Notes due April 2024 [Member]</link:label>
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    <link:label id="lab_dgx_FourpointtwofivepercentSeniorNotesDue2024Member_8B76B43A42CEFF8BA452AF31C7E83C1C_documentation_en-US" xlink:label="lab_dgx_FourpointtwofivepercentSeniorNotesDue2024Member_8B76B43A42CEFF8BA452AF31C7E83C1C" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Four point two five percent Senior Notes Due 2024 [Member]</link:label>
    <link:loc xlink:href="dgx-20150930.xsd#dgx_FourpointtwofivepercentSeniorNotesDue2024Member" xlink:label="loc_dgx_FourpointtwofivepercentSeniorNotesDue2024Member_8B76B43A42CEFF8BA452AF31C7E83C1C" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dgx_FourpointtwofivepercentSeniorNotesDue2024Member_8B76B43A42CEFF8BA452AF31C7E83C1C" xlink:to="lab_dgx_FourpointtwofivepercentSeniorNotesDue2024Member_8B76B43A42CEFF8BA452AF31C7E83C1C" xlink:type="arc" />
    <link:label id="lab_dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member_1AA861D230331AE67C08AF31C7E84DDD_terseLabel_en-US" xlink:label="lab_dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member_1AA861D230331AE67C08AF31C7E84DDD" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">3.50% Senior Notes due March 2025 [Member]</link:label>
    <link:label id="lab_dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member_1AA861D230331AE67C08AF31C7E84DDD_label_en-US" xlink:label="lab_dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member_1AA861D230331AE67C08AF31C7E84DDD" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Three Point Five Zero Percent Senior Notes due March 2025 [Member]</link:label>
    <link:label id="lab_dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member_1AA861D230331AE67C08AF31C7E84DDD_documentation_en-US" xlink:label="lab_dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member_1AA861D230331AE67C08AF31C7E84DDD" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Three Point Five Zero Percent Senior Notes due March 2025 [Member]</link:label>
    <link:loc xlink:href="dgx-20150930.xsd#dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member" xlink:label="loc_dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member_1AA861D230331AE67C08AF31C7E84DDD" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member_1AA861D230331AE67C08AF31C7E84DDD" xlink:to="lab_dgx_ThreePointFiveZeroPercentSeniorNotesdueMarch2025Member_1AA861D230331AE67C08AF31C7E84DDD" xlink:type="arc" />
    <link:label id="lab_dgx_SixPointNineFivePercentSeniorNotesDue2037Member_AB4EA62B96C8AC51D442AF31C7E88211_terseLabel_en-US" xlink:label="lab_dgx_SixPointNineFivePercentSeniorNotesDue2037Member_AB4EA62B96C8AC51D442AF31C7E88211" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">6.95% Senior Notes Due 2037 [Member]</link:label>
    <link:label id="lab_dgx_SixPointNineFivePercentSeniorNotesDue2037Member_AB4EA62B96C8AC51D442AF31C7E88211_label_en-US" xlink:label="lab_dgx_SixPointNineFivePercentSeniorNotesDue2037Member_AB4EA62B96C8AC51D442AF31C7E88211" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Six Point Nine Five Percent Senior Notes Due2037 [Member]</link:label>
    <link:label id="lab_dgx_SixPointNineFivePercentSeniorNotesDue2037Member_AB4EA62B96C8AC51D442AF31C7E88211_documentation_en-US" xlink:label="lab_dgx_SixPointNineFivePercentSeniorNotesDue2037Member_AB4EA62B96C8AC51D442AF31C7E88211" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Six Point Nine Five Percent Senior Notes Due 2037 [Member]</link:label>
    <link:loc xlink:href="dgx-20150930.xsd#dgx_SixPointNineFivePercentSeniorNotesDue2037Member" xlink:label="loc_dgx_SixPointNineFivePercentSeniorNotesDue2037Member_AB4EA62B96C8AC51D442AF31C7E88211" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dgx_SixPointNineFivePercentSeniorNotesDue2037Member_AB4EA62B96C8AC51D442AF31C7E88211" xlink:to="lab_dgx_SixPointNineFivePercentSeniorNotesDue2037Member_AB4EA62B96C8AC51D442AF31C7E88211" xlink:type="arc" />
    <link:label id="lab_dgx_FivePointSevenFivePercentSeniorNotesDue2040Member_722C373497C770833E15AF31C7E8D47A_terseLabel_en-US" xlink:label="lab_dgx_FivePointSevenFivePercentSeniorNotesDue2040Member_722C373497C770833E15AF31C7E8D47A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">5.75% Senior Notes Due 2040 [Member]</link:label>
    <link:label id="lab_dgx_FivePointSevenFivePercentSeniorNotesDue2040Member_722C373497C770833E15AF31C7E8D47A_label_en-US" xlink:label="lab_dgx_FivePointSevenFivePercentSeniorNotesDue2040Member_722C373497C770833E15AF31C7E8D47A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Five Point Seven Five Percent Senior Notes Due2040 [Member]</link:label>
    <link:label id="lab_dgx_FivePointSevenFivePercentSeniorNotesDue2040Member_722C373497C770833E15AF31C7E8D47A_documentation_en-US" xlink:label="lab_dgx_FivePointSevenFivePercentSeniorNotesDue2040Member_722C373497C770833E15AF31C7E8D47A" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Five Point Seven Five Percent Senior Notes Due 2040 [Member]</link:label>
    <link:loc xlink:href="dgx-20150930.xsd#dgx_FivePointSevenFivePercentSeniorNotesDue2040Member" xlink:label="loc_dgx_FivePointSevenFivePercentSeniorNotesDue2040Member_722C373497C770833E15AF31C7E8D47A" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_dgx_FivePointSevenFivePercentSeniorNotesDue2040Member_722C373497C770833E15AF31C7E8D47A" xlink:to="lab_dgx_FivePointSevenFivePercentSeniorNotesDue2040Member_722C373497C770833E15AF31C7E8D47A" xlink:type="arc" />
    <link:label id="lab_dgx_FourPointSevenZeroPercentSeniorNotesdueMarch2045Member_9544F9EA982500441189AF31C7E82E8E_terseLabel_en-US" xlink:label="lab_dgx_FourPointSevenZeroPercentSeniorNotesdueMarch2045Member_9544F9EA982500441189AF31C7E82E8E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">4.70% Senior Notes due March 2045 [Member]</link:label>
    <link:label id="lab_dgx_FourPointSevenZeroPercentSeniorNotesdueMarch2045Member_9544F9EA982500441189AF31C7E82E8E_label_en-US" xlink:label="lab_dgx_FourPointSevenZeroPercentSeniorNotesdueMarch2045Member_9544F9EA982500441189AF31C7E82E8E" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Four Point Seven Zero Percent Senior Notes due March 2045 [Member]</link:label>
    <link:label id="lab_dgx_FourPointSevenZeroPercentSeniorNotesdueMarch2045Member_9544F9EA982500441189AF31C7E82E8E_documentation_en-US" xlink:label="lab_dgx_FourPointSevenZeroPercentSeniorNotesdueMarch2045Member_9544F9EA982500441189AF31C7E82E8E" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Four Point Seven Zero Percent Senior Notes due March 2045 [Member]</link:label>
    <link:loc xlink:href="dgx-20150930.xsd#dgx_FourPointSevenZeroPercentSeniorNotesdueMarch2045Member" xlink:label="loc_dgx_FourPointSevenZeroPercentSeniorNotesdueMarch2045Member_9544F9EA982500441189AF31C7E82E8E" xlink:type="locator" />
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    <link:label id="lab_dgx_OtherLongTermDebtMember_E7A9C06CE7BF5266F901AF31C7E873FA_documentation_en-US" xlink:label="lab_dgx_OtherLongTermDebtMember_E7A9C06CE7BF5266F901AF31C7E873FA" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Other Long-term Debt [Member]</link:label>
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    <link:label id="lab_us-gaap_RangeAxis_D4E708EE40EC88B0E488AF31C7E81526_label_en-US" xlink:label="lab_us-gaap_RangeAxis_D4E708EE40EC88B0E488AF31C7E81526" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Range [Axis]</link:label>
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    <link:label id="lab_us-gaap_AssetsCurrent_148E153DF9E84481EF6AABA529B238D6_totalLabel_en-US" xlink:label="lab_us-gaap_AssetsCurrent_148E153DF9E84481EF6AABA529B238D6" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Total current assets</link:label>
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    <link:label id="lab_us-gaap_ShareBasedCompensation_05363D42A01DD34F5E63ABA5299E970A_terseLabel_en-US" xlink:label="lab_us-gaap_ShareBasedCompensation_05363D42A01DD34F5E63ABA5299E970A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Stock-based compensation expense</link:label>
    <link:label id="lab_us-gaap_ShareBasedCompensation_05363D42A01DD34F5E63ABA5299E970A_label_en-US" xlink:label="lab_us-gaap_ShareBasedCompensation_05363D42A01DD34F5E63ABA5299E970A" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Share-based Compensation</link:label>
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    <link:label id="lab_us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities_ACCC37116A9D1A123BC1ABA5299EDE95_negatedLabel_en-US" xlink:label="lab_us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities_ACCC37116A9D1A123BC1ABA5299EDE95" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Excess tax benefits from stock-based compensation arrangements</link:label>
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    <link:label id="lab_us-gaap_OtherNoncashIncomeExpense_3D77C7917A5EE25914EEABA5299FC70E_negatedLabel_en-US" xlink:label="lab_us-gaap_OtherNoncashIncomeExpense_3D77C7917A5EE25914EEABA5299FC70E" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Other, net</link:label>
    <link:label id="lab_us-gaap_OtherNoncashIncomeExpense_3D77C7917A5EE25914EEABA5299FC70E_label_en-US" xlink:label="lab_us-gaap_OtherNoncashIncomeExpense_3D77C7917A5EE25914EEABA5299FC70E" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Other Noncash Income (Expense)</link:label>
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    <link:label id="lab_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0E7511E032323679FE7AABA5299F8232_label_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_0E7511E032323679FE7AABA5299F8232" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Increase (Decrease) in Operating Capital [Abstract]</link:label>
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    <link:label id="lab_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_9598C2464F3962D27B89ABA5299F2A07_negatedLabel_en-US" xlink:label="lab_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_9598C2464F3962D27B89ABA5299F2A07" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Other assets and liabilities, net</link:label>
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_8DCD27386F8204B99441ABA5299FB737_totalLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInOperatingActivities_8DCD27386F8204B99441ABA5299FB737" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Net cash provided by operating activities</link:label>
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4632D2AB5E238199E1FFABA5299FF871_label_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_4632D2AB5E238199E1FFABA5299FF871" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Net Cash Provided by (Used in) Investing Activities [Abstract]</link:label>
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    <link:label id="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_27BC5A925840B78AE9B9ABA5299FC254_terseLabel_en-US" xlink:label="lab_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_27BC5A925840B78AE9B9ABA5299FC254" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Cash flows from investing activities:</link:label>
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    <link:label id="lab_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_0EE3BFB7D0AF11C3B26FABA529A0DFF9_negatedLabel_en-US" xlink:label="lab_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_0EE3BFB7D0AF11C3B26FABA529A0DFF9" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:type="resource" xml:lang="en-US">Business acquisitions, net of cash acquired</link:label>
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