Document

We have acted as counsel to Exagen Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing by the Company of a Registration Statement on Form S-3 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”) with the Securities and Exchange Commission (the “Commission”). The Registration Statement relates to the registration for the offer and sale of shares of the Company’s common stock issuable upon the exercise of an outstanding warrant certificate (the “Warrant Certificate”) to purchase up to an aggregate of 1,150,000 shares the Company’s common stock (the “Warrant Shares”), which was originally issued by the Company in connection with that certain Credit Agreement and Guaranty dated as of April 25, 2025, by and between the Company and Perceptive Credit Holdings IV, LP as lender and administrative agent.

In connection with this opinion, we have examined the Company’s Amended and Restated Certificate of Incorporation, and Amended and Restated Bylaws, each as restated and/or amended to date and currently in effect; such other records of the corporate proceedings of the Company and certificates of the Company’s officers as we have deemed relevant; and the Registration Statement and the exhibits thereto.

In our examination, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as certified or photostatic copies and the authenticity of the originals of such copies, and the truth and correctness of any representations and warranties contained therein.

Our opinion is expressed only with respect to the General Corporation Law of the State of Delaware. We express no opinion to the extent that any other laws are applicable to the subject matter hereof and express no opinion and provide no assurance as to compliance with any federal or state securities law, rule or regulation.

With respect to the Warrant Shares, we express no opinion to the extent that future issuances of securities of the Company, adjustments to outstanding securities of the Company and/or other matters cause the Warrant Certificate to be exercisable for more shares of Common Stock than the number that remain available for issuance. Further, we have assumed the exercise price of the Warrant Certificate will not be adjusted to an amount below the par value per share of the Common Stock.

Based upon and subject to the foregoing, it is our opinion that the Warrant Shares, when issued against payment therefor in accordance with the terms of the Warrant Certificate, will be validly issued, fully paid and non-assessable.

Please note that we are opining only as to the matters expressly set forth herein, and no opinion should be inferred as to any other matters. This opinion is based upon currently existing statutes, rules, regulations and judicial decisions, and we disclaim any obligation to advise you of any change in any of these sources of law or subsequent legal or factual developments which might affect any matters or opinions set forth herein.

We understand that you wish to file this opinion with the Commission as an exhibit to the Registration Statement in accordance with the requirements of Item 601(b)(5) of Regulation S-K promulgated under the Securities Act and to reference the firm’s name under the caption “Legal Matters” in the prospectus which forms part of the Registration Statement, and we hereby consent thereto. In giving this consent, we do not admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission promulgated thereunder.


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BOSTON LOS ANGELES MIAMI NEW YORK SAN DIEGO SAN FRANCISCO TORONTO WASHINGTON MINTZ, LEVIN, COHN, FERRIS, GLOVSKY AND POPEO, P.C.


Very truly yours,


/s/ Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.


MINTZ June 20, 2025 Page 2