UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF

THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of Earliest Event Reported): April 27, 2026

Quest Diagnostics Incorporated

(Exact Name of Registrant as Specified in Its Charter)

Delaware

(State or other jurisdiction of incorporation)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company   ¨

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.       ¨

Item 8.01 Other Events

On April 27, 2026, Quest Diagnostics Incorporated (the “Company”) issued a press release announcing the pricing of a public offering of $500 million aggregate principal amount of its 5.000% senior notes due 2036 (the “Notes”) under the Company’s shelf registration statement. The Company intends to use the net proceeds from the offering for general corporate purposes, which may include the repayment of indebtedness. The indebtedness the Company may repay includes its $500 million aggregate principal amount of 3.45% Senior Notes that mature on June 1, 2026. The Company expects to receive the net proceeds upon closing of the offering on May 6, 2026, subject to customary closing conditions. A copy of the press release, dated April 27, 2026, is attached to this Current Report on Form 8-K as Exhibit 99.1 and is incorporated by reference into this Current Report on Form 8-K.

In connection with the offering of the Notes, on April 27, 2026, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Goldman Sachs & Co. LLC, J.P. Morgan Securities LLC and Mizuho Securities USA LLC on behalf of themselves and the other underwriters named therein. The Underwriting Agreement is attached to this Current Report on Form 8-K as Exhibit 1.1 and is incorporated by reference into this Current Report on Form 8-K.

Item 9.01 Financial Statements and Exhibits

Signature

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, hereunto duly authorized.

May 1, 2026