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Medically Unlikely Edits

MUEs were developed by CMS in January 2007, as part of the effort to reduce the paid claims error rate for Medicare claims. These edits were developed with clinical input from both CMS and the MACs, and were set to define the maximum UOS that a provider would reasonably report for a single beneficiary on a single date of service.

In April 2013, CMS modified the MUE program by introducing a new data field to the MUE edit table, termed “MUE Adjudication Indicator” or “MAI.” CMS updates the MUE/MAI edit tables quarterly (in January, April, July and October), so providers need to remain aware that new values may impact claim payments after each update cycle.

MUEs are not yet in place for all HCPCS/CPT codes, and most MUEs with MAI values of 1-3 are published on the CMS website. There are a number of confidential MUE values that CMS does not choose to publish. Providers are advised to administer and bill for the number of medically necessary units relative to any service or drug, whether an MUE limit is published or not. If a claim denies on an MUE edit (published or nonpublished) the provider is free to submit an appeal with medical documentation of the need for the number of services billed.

The following describes the way that MAI designations impact claim processing:

  • MAI Indicator “1”: this is a claim line edit which will deny when UOS are in excess of the MUE, although this may be impacted by the presence of a modifier on the claim line.


    Provider billed 88350 for 8 units on one line, (the MUE is 4) and the claim denies. Instead the provider should have billed on two lines, the first with UOS 4 and the second with UOS 4 and a 76/77 modifier to identify additional services. A denial of this type can usually be corrected via the reopening process and may not require a formal redetermination request.
  • MAI Indicator “2”: this is an absolute date of service edit. UOS in excess of the MUE value would be considered impossible because of a statute, regulation or subregulatory guidance. This includes Correct Coding policy that is binding for both providers and MACs.


    It would be incorrect to report more than one unit of service for (CPT) 94002 "ventilation assist and management . . . initial day", since this code describes all care on a particular DOS.

    Note: When physician’s bill for bilateral services and the MAI value is 2, they must bill as a single line item with the 50 modifier.
  • MAI Indicator “3”: this is a date of service edit based on clinical benchmarks. If medical necessity for the excess UOS is established through prepayment review of the claim, reopening or redetermination process, or through instructions from a higher level of appeal, MACs may bypass these edits and allow the excess UOS.

    Note: UOS are counted for all lines of service on the current claim and any prior finalized claim for the same DOS. When that count exceeds the MUE UOS, all claim lines for the code on the current claim are denied, although prior paid and finalized claims are not adjusted.

Notes on MUE Processing Instructions

  • Since MUEs are auto-deny edits, denials may be appealed to the MAC. Upon review of medical records via the redetermination process, the MAC may allow excess UOS based on assessment of medical necessity. Denials based on coding or billing errors can often be addressed via the reopening process.
  • MUEs are prospective edits, applicable to the time period for which they are effective. Changes in MUES are not retrospective and do not apply to prior services. In the unusual event of a retroactive MUE, providers would be expected to bring impacted claims to the attention of the MAC for adjustment.
  • MUE denials are coding denials, not medical necessity denials. Liability cannot be shifted to the beneficiary, even in the presence of an ABN. ABN issuance based on an anticipated MUE denial is not appropriate.
  • For ambulatory surgical centers (ASC, specialty code 49): when a bilateral surgery indicator for the HCSPCS code is “1”, the MUE value will be doubled when the MAI is “2” or “3,” since ASCs cannot report modifier 50
  • CMS encourages providers to change and resubmit their own claims where possible and to change their coding practices. During the reopening process, MACs may, when necessary, correct the claim to modifier 50 from an equivalent 2 units of bilateral anatomic modifiers. CMS also reminds providers to use anatomic modifiers (e.g., RT, LT, FA, F1-F9, TA, T1-T9, E1-E4) and report procedures with differing modifiers on individual claim lines when appropriate. Many MUEs are based on the assumption that correct modifiers are used.
  •  Remittance Advice statements will continue to use Group Code CO (contractual obligation), and remark codes N362 and MA01 for claims that fail the MUE edits. When the UOS on the claim exceed the MUE value, MACs will deny the entire claim line(s) for the relevant HCPCS code.

Inquiries on MUE Editing

  • Inquiries about the MUE program other than those related to MUE values for specific HCPCS/CPT codes should be sent to the email address
  • If a provider or healthcare organization believes that an MUE value should be modified, you may write Correct Coding Solutions, LLC. Please include its rationale and any supporting documentation. 
  • Requests for modification of an MUE value should be sent to the following:

National Correct Coding Initiative
Correct Coding Solutions, LLC
P.O. Box 907
Carmel, IN 46082-0907
Fax: 317-571-1745

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