MUEs and Bilateral Indicators

March 23rd, 2023 - Chris Woolstenhulme

MUEs are used by Medicare to help reduce improper payments for Part B claims. This article will address the use of the National Correct Coding Initiative (NCCI) and Medically Unlikely Edits (MUEs), how they are used by CMS, and the relationship to Medicare Physician Fee Schedule (MPFS) Indicators.  MUEs are applied to Healthcare Common Procedure Coding System (HCPCS) and Current Procedural Terminology (CPT) codes to indicate the maximum number of units commonly used on a single date of service.    

CMS assigns Medically Unlikely Edits (MUEs) to most HCPCS/CPT codes used under part B for Practitioner Services, Outpatient Hospital Services, and DME Supplier Services. However, not every code has an MUE assigned.  According to CMS, MUE edits are used to limit tests and treatments provided to a Medicare patient for a single date of service or for a single line item on a claim form. In order to code correctly, it is important to understand how payers adjudicate your claims; this is the intent of this article.  Even if you are not billing a Medicare claim, keep in mind most payers follow Medicare's rules and guidelines. 

MUEs are not Utilization Guidelines!

First of all, it is important to understand that MUEs are not to be used as utilization guidelines; CMS is concerned that providers will incorrectly interpret MUE values as utilization guidelines. Utilization guidelines pertain to medical necessity, and CMS states providers should only report services that are medically reasonable and necessary. However, if the number of units is over the maximum number of allowed MUEs, and is medically necessary, the provider should report what is needed.  CMS offers additional guidance and more detailed information in their article MLN MM8853- Revised Modification to the Medically Unlikely Edit (MUE) Program. Without getting too deep in the weeds, each MUE is further assigned an adjudication indicator or (MAI) which determines additional usage; see the list below from CGS - Medically Unlikely Edits. As you can see in the list, if an MUE is assigned an MAI 3, the claim may be reconsidered with adequate documentation.

MUE Adjudication Indicator (MAI)

The MAI provides the rationale for the edit.

  • MAI 1: Claim Line Edit. 
    • You may add a modifier to bill the same code on separate lines of a claim to identify additional medically necessary units over the MUE value.
  • MAI 2: Absolute Date of Service Edit. 
    • These are "per day" edits based on policy. CGS will not pay in excess of the MUE value.
  • MAI 3: Date of Service Edit. 
    • These are "per day" edits based on clinical benchmarks. CGS may pay over the MUE value at the appeals (Redetermination) level if there is adequate documentation of medical necessity to support additional units.

According to CMS, although CMS publishes most MUE values on its website, other MUE values are confidential.  Confidential MUE values are not releasable. 

Find-A-Code lists the MUE values that have been released by CMS; these MUEs can be found on the CPT code information page under the additional information tab for easy access. 

Reminder: MUEs are used on a case-by-case basis and are not to be used as utilization guidelines. In other words, if your clinical data reflects the need for additional units and it is medically reasonable and necessary, it should be reported.

MUE Usage Rationale 

  • Published Contractor Policy
  • CMS Policy
  • Clinical: Data
  • Nature of Equipment 

Durable Medical MUEs
CMS also assigns MUEs to durable medical equipment using HCPCS codes, as mentioned above.  

56 MUEs have been assigned to HCPCS code A4218 - Sterile saline or water, metered dose dispenser, 10 ml. 

1- MUE has been assigned to HCPCS code (notice the description states 1 month supply = 1 unit of service) A4238 - Supply allowance for adjunctive, non-implanted continuous glucose monitor (cgm), includes all supplies and accessories, 1 month supply = 1 unit of service

NOTE: Incorrect usage of MUEs will be denied as a coding denial, not a clinical or medically necessary denial. 

Claim Remark Codes 

On your EOB or remittance advice, to identify claims that fail the MUE edit claim, remark codes N362 and MA01 will be used.   

Bilateral Procedures and MUEs
You may be wondering how MUEs work with bi-lateral procedures, good question. We first need to understand Medicare's correct coding instructions; we are required to report a bilateral procedure with a 50 Modifier and one Unit of Service (UOS) on the same line. To understand if a procedure can be performed bilaterally, pay careful attention to the following. 

The code description: Always start here; the code may state in the description if the procedure is bilateral or unilateral, for example, 27395 - Lengthening of hamstring tendon: multiple tendons, bilateral. If the code includes bilateral, then there are no changes in the fee schedule payment as the work is already considered in the fee as indicated in the description.  

Bilateral Indicator: Medicare uses what is called Medicare Physician Fee Schedule (MPFS) indicators. One indicator is called a Bilateral Surgery Indicator, letting us know whether special payment rules apply, such as the 150% payment rule for a bilateral procedure. The bilateral surgery indicator lets us know if modifier 50 is allowed to be reported with the procedure/CPT code. Let's take a look at the same CPT code, 27395- Lengthening of hamstring tendon: multiple tendons, bilateral.  CMS has assigned a bilateral Surgery indicator of "2," indicating the 150% payment adjustment for bilateral surgery does NOT apply. Therefore, you cannot code this procedure with Modifier 50, as the code already includes a bilateral procedure in the description. 

Bilateral Indicator Description
0 No bilateral payment adjustment:  (a) because of physiology or anatomy, or (b) because the code description specifically states that it is a unilateral procedure, and there is an existing code for the bilateral procedure. 
1 150% Bilateral payment adjustment applies: If the code is billed with the bilateral modifier or is reported twice on the same day by any other means (e.g., with RT and LT modifiers or with a 2 in the units field), base the payment for these codes when reported as bilateral procedures on the lower of (a) the total actual charge for both sides or (b) 150% of the fee schedule amount for a single code. If the code is reported as a bilateral procedure and is reported with other procedure codes on the same day, apply the bilateral adjustment before applying any multiple procedure rules. 
2 150% payment adjustment does not apply. Bilateral surgery rules do not apply. Already priced as bilateral. Do not use 50 modifier. Units = 1.
3 Bilateral surgery rules do not apply. Do not use 50 modifier. Units = 1 or 2.
9 Bilateral surgery concept does not apply.

Here are some examples showing how CMS processes claims under part "B"  according to Noridian. 

  • CPT 27331 has a bilateral indicator of a 1, which means bilateral surgery rules apply. If the 50 modifier is appended to the CPT with 1 unit billed, Medicare will allow 150%. If billed with 2 units, it states the procedure was completed 4 times and will be denied as unprocessable. If two of the same services were performed bilaterally, the services should be billed on two separate lines with 1 unit apiece, the 50 modifier, and the appropriate repeat modifier on one of the lines.
  • CPT 28340 has a bilateral indicator of 0. Bilateral surgery rules do not apply, and modifier 50 is not to be used.
  • CPT 27395 has a bilateral indicator of a 2, which means bilateral surgery rules do not apply. These procedures are already priced for either unilateral or bilateral performance. It would be inappropriate to bill the procedure with the 50 modifier as a bilateral service. Also, it would be inappropriate when billed on 2 lines or with 2 units if only one service was performed, even when using RT and LT modifiers.

Codes with a 2 indicator are already priced at 150%, which means Medicare is already paying for both sides. If billed on two lines or with two units, the total allowed amount will be 300% instead of 150%. This would be incorrect billing if only one service was performed.

For additional details, see "Examples of Correct Coding for Bilateral Procedures, see MLN SE142."
Reporting RT and LT modifiers
So how do we address the use of RT and LT modifiers? The modifiers will still be used for identifying which side of the body the procedure was performed on. However, the modifiers are not used to indicate bilateral if the reported procedure already includes unilateral or bilateral. For example, 52290, Cystourethroscopy, with ureteral meatotomy, unilateral or bilateral52290 has a surgery bilateral indicator 2, yet we still need to identify which side the procedure was performed on; however, we know it is not appropriate to report more than one unit of service (UOS) when a code is assigned with the bilateral indicator 2. In addition, it is inappropriate to report two lines, as the description already includes payment for either unilateral or bilateral, in the description as well as in the Bilateral surgery indicator 2. Therefore we would report 52290 with one unit and indicate RT and or LT if bilateral on the same line item. 

Procedure, services, or supplies Modifier Unit of Service
52290 RT, LT 1

For claim-specific questions, contact your MAC representative. If your questions are about the MUE program or questions related to NCCI (PTP, MUE, and Add-On) edits, send them to

Appeals and Reconsideration
According to HHS, If a national healthcare organization, provider, or other party wants to submit a request for reconsideration of an MUE value, the procedure described in the Frequently Asked Questions (FAQs) should be followed.  See the web link below.  Such requests should be addressed to:

National Correct Coding Initiative



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