奎斯特诊疗美股招股说明书(2026-04-28版)

$500,000,000 5.000% senior notes due 2036 We are offering $500,000,000 aggregate principal amount of 5.000% senior notes due 2036 (the “notes”). The notes willmature on June30, 2036. We will pay interest on the notes semiannually on June 30 and December 30 of each year, beginning December 30, 2026. We may redeem some or all of the notes at any time at the applicable redemption prices described in this prospectussupplement. The notes will be senior unsecured obligations of ours and will rank equally with our other existing and future seniorunsecured obligations. The notes will be issued only in registered form in minimum denominations of $2,000 and integralmultiples of $1,000 in excess thereof. Investing in the notes involves risks that are described in the “Risk Factors” section of ourAnnual Report on Form10-K for theyear ended December31, 2025, as may be amended, updated or modified in our reports filed with the Securities and ExchangeCommission, which are incorporated by reference into this prospectus supplement, and in the “Risk Factors” section beginning onpageS-5of this prospectus supplement. Per noteTotalPublic offering price98.751$493,755,000Underwriting discount0.650$3,250,000Proceeds, before expenses, to us98.101$490,505,000(1)%%% (1)Plus accrued interest from May 6, 2026, if settlement occurs after that date. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of thesesecurities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation tothe contrary is a criminal offense. We do not intend to apply for listing of the notes on any securities exchange. Currently, there is no public trading market for thenotes. The notes will be ready for delivery in book-entry form only through the facilities of The Depository Trust Company for theaccounts of its participants, including Euroclear Bank S.A./N.V., as operator of the Euroclear System, and Clearstream Banking,société anonyme, on or about May 6, 2026. Joint Book-Running Managers BofA Securities The date of this prospectus supplement is April 27, 2026 Table of contents Prospectus supplementSummaryS-1Risk factorsS-5Cautionary statement for purposes of the “safe harbor” provisions of the Private SecuritiesLitigation Reform Act of 1995S-6Use of proceedsS-9CapitalizationS-10Description of notesS-11United States federal income tax considerationsS-28Underwriting (conflicts of interest)S-32Legal mattersS-36ExpertsS-36Where you can find more informationS-36ProspectusAbout this prospectusiiWhere you can find more informationiiCautionary statement for purposes of the “safe harbor” provisions of the Private SecuritiesLitigation Reform Act of 1995ivProspectus summary1Risk factors2Use of proceeds3Securities we may issue4Description of senior debt securities5Plan of distribution7Validity of the securities8Experts8 Neither we nor the underwriters have authorized anyone to provide you with any information or tomake any representation not contained in or incorporated by reference into this prospectus supplement orthe accompanying prospectus or included in any free writing prospectus that we may file with the Securitiesand Exchange Commission (the “SEC”) in connection with this offering. Neither we nor the underwriterstake any responsibility for, or can provide any assurances as to, the reliability of any information that othersmay provide you. Neither we nor the underwriters are making an offer to sell these securities in anyjurisdiction where the offer or sale is not permitted. You should assume that the information appearing inthis prospectus supplement, the accompanying prospectus and the documents incorporated by reference isaccurate only as of their respective dates. Our business, financial condition, cash flows, results of operationsand prospects may have changed since these dates. About this prospectus supplement This document has two parts. The first part consists of this prospectus supplement, which describes thespecific terms of this offering and the notes offered. The second part, the accompanying prospectus,provides more general information, some of which may not apply to this offering. If the description of theoffering varies between this prospectus supplement and the accompanying prospectus, you should rely onthe information in this prospectus supplement. Before purchasing any notes, you should carefully read both this prospectus supplement and theaccompanying prospectus, together with the additional information described under the heading “WhereYou Can Find More Information” in this prospectus supplement. Unless otherwise stated or where the context otherwise requires, references in this prospectussupplement to “we,” “us,” “our” and the “Company” are to Quest Diagnostics Incorporated and itsconsolidated subsidiaries and references to “Quest Diagnostics” are to Quest Diagnostics Incorporated onlyand not to any of its sub