What do Medicare Beneficiary Identifiers (MBIs) mean for health care providers & office managers?

Using the Medicare Beneficiary Identifiers (MBIs), helps to protect the identities of people with Medicare and keep them safer from identity theft.

Even though we're not using Social Security Numbers (SSNs) to identify Medicare beneficiaries any more, your own Social Security Number is still used by the Social Security Administration, by the Internal Revenue Service (IRS), and for tax reasons, like on your W-9.

Where can health care providers & office managers get more information about MBIs?

• Find more details if you’re a Medicaid, supplemental insurer, or other private payer.
• Find tips for successfully using the MBI, what to do if an MBI changes, and more in our MLN Matters article, "New Medicare Beneficiary Identifier (MBI) Get It, Use It (PDF)".
• Get materials from our past Open Door Forums. 
• Read our frequently asked questions (PDF).

You can also check our Outreach & education page for resources about getting and using the MBI.

What should I do if my patient's MBI changes?

Medicare beneficiaries or their authorized representatives can ask to change their MBIs; for example, if the MBI is compromised. CMS can also change an MBI. It's possible for your patient to seek care before getting a new card with the new MBI. 

If you get a HETS eligibility transaction error code (AAA 72) of “invalid member ID,” your patient’s MBI may have changed.  

• Do a historic eligibility search to get the termination date of the old MBI.
• Get the new MBI from your Medicare Administrative Contractor’s secure MBI look-up tool. Sign up (PDF) for the Portal to use the tool.

When to use old or new MBIs:

Fee-For-Service (FFS) claims submissions with:

• Dates of service before the MBI change date – use old or new MBIs
• Span-date claims with a “From Date” before the MBI change date – use old or new MBIs
• Dates of service that are entirely on or after the effective date of the MBI change – use new MBIs

FFS eligibility transactions when the inquiry uses:

• A new MBI – we'll return all eligibility data.
• The old MBI and request date or date range overlap the active period for the old MBI – we'll return all eligibility data. We will also return the old MBI termination date.
• The old MBI and request date or date range are entirely on or after the effective date of the new MBI – we'll return an error code (AAA 72) of “invalid member ID.”

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