EXHIBIT 3.31

CERTIFICATE OF AMENDMENT

TO THE

CERTIFICATE OF INCORPORATION

OF

AMERICAN RENAL HOLDINGS COMPANY, INC.

March 8, 2011

American Renal Holdings Company, Inc., a corporation organized and existing under the laws of the State of Delaware (the “Corporation”), hereby certifies as follows:

1. The name of the Corporation is American Renal Holdings Company, Inc.

2. The original Certificate of Incorporation of the Corporation was filed with the Secretary of State of the State of Delaware under the name C.P. Atlas Holdings, Inc. on March 18, 2010 (as amended and restated through the date hereof, the “Certificate of Incorporation”).

3. This Certificate of Amendment, which amends the Certificate of Incorporation, was duly adopted in accordance with Sections 228 and 242 of the General Corporation Law of the State of Delaware.

4. Article First of the Certificate of Incorporation is hereby amended to read in its entirety as follows:

“FIRST: The name of the corporation (which is hereinafter referred to as the “Corporation”) is American Renal Associates Holdings, Inc.”

5. This Certificate of Amendment shall be effective as of the date of its filing with the Secretary of State of the State of Delaware.

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IN WITNESS WHEREOF, the undersigned, as a duly authorized officer of the Corporation, has executed this Certificate of Amendment as of the first date set forth above.