Bundled Denial in Medical Billing

What happens when several procedures are performed during the same visit, but the insurance payer decides they should be billed as one service instead of multiple? This leads to a situation that is known as a bundled denial in medical billing.

Bundled denials are a significant driver of that number. And unlike most denials, they are almost entirely preventable if your team understands the rules.

This guide breaks down every dimension of bundled denial: what it means, what causes it, how the NCCI edit system works in 2026, which modifiers can override bundling, how to appeal effectively, and what best-in-class billing operations do differently.

What Is a Bundled Denial in Medical Billing?

A bundled denial occurs when a payer refuses to separately reimburse a procedure or service because it is considered already included in the payment for another, more comprehensive service billed on the same claim. The payer essentially says, “We already paid for that when we paid for the primary procedure.”

The most common denial code associated with bundling is CO-97 (Claim Adjustment Reason Code 97): “The benefit for this service is included in the payment/allowance for another service/procedure that has already been adjudicated.”

This is a Contractual Obligation (CO) denial, meaning the provider, not the patient, absorbs the adjustment. Billing the patient for a CO-adjusted amount directly violates provider agreements with payers and can trigger audits and recoupment demands.

Bundling vs. Unbundling 

These two terms describe opposite sides of the same coding error:

Bundling (the payer’s action) 

Combining separately billed services into one reimbursable unit results in the denial of the secondary code.

Unbundling (a provider billing error or fraud) 

It means splitting services that should be billed under a single comprehensive code into multiple individual codes to inflate reimbursement.

Unbundling is flagged and prevented by CMS’s National Correct Coding Initiative (NCCI). When CPT codes are reported that should legally be bundled, the NCCI edit system denies payment on the secondary code automatically.

What Is the NCCI and Why Does It Exist?

The National Correct Coding Initiative (NCCI) was created by the Centers for Medicare & Medicaid Services (CMS) to prevent improper payment when incorrect code combinations are submitted. It is the primary automated mechanism behind most bundled denials in Medicare and Medicaid billing.

According to CMS’s official NCCI FAQ Library, the NCCI system contains three main edit types:

1. Procedure-to-Procedure (PTP) Edits — prevent payment when two codes that should not be billed together are submitted for the same beneficiary on the same date of service.
2. Medically Unlikely Edits (MUEs) — limit the maximum units of service for a given HCPCS/CPT code per claim per day.
3. Add-on Code (AOC) Edits — govern codes that can only be billed alongside a specified primary procedure.

How PTP Edits Work

Every PTP edit pairs a Column One code with a Column Two code. When both are submitted for the same patient on the same date:

• The Column One code is eligible for payment.
• The Column Two code is denied unless an appropriate NCCI-associated modifier is attached and clinically justified.

Each PTP edit pair carries a Modifier Indicator:

• Indicator 0: The two codes should never be billed together. No modifier can override the denial.
• Indicator 1: A modifier may be used to override the edit if the services were truly distinct.

As of April 1, 2026, CMS posted updated PTP edit files (Version 32.1) containing over 675,000 practitioner edit pairs and over 475,000 hospital outpatient edit pairs, per the CMS NCCI PTP Edits page (posted March 2, 2026). These files are updated quarterly.Q1 and Q2 2026 edits are already active.

Medically Unlikely Edits (MUEs) 

MUEs prevent payment for an unreasonable quantity of the same service in a single day. Each MUE has a MUE Adjudication Indicator (MAI):

• MAI 1: Date-of-service edit adjudicated at the line level.
• MAI 2: Date-of-service edit adjudicated at the claim level.

A critical compliance note from CMS: 

An Advance Beneficiary Notice (ABN) cannot be used to shift liability to the beneficiary for MUE denials. These are coding denials, not medical necessity denials, and the provider absorbs the adjustment.

What are the Common Reasons of Bundled Denials?

Here are a few reasons why bundled denials occur:

Billing Component Codes with a Comprehensive Code

The most classic bundling scenario: billing individual component services when a single comprehensive CPT code already covers all of them. For example, billing each test in a Basic Metabolic Panel (CPT 80048) separately, rather than using the panel code. The NCCI edits specifically govern this — laboratory panel codes bundle the individual chemistry tests within them.

Billing Surgical Components Separately

Many surgical procedures include pre-operative, intra-operative, and post-operative components within their global surgical package. When billers attempt to separately report services already included in the global package — such as routine wound closure after an open procedure — the claim triggers a bundling denial.

Per the NCCI Policy Manual, HCPCS/CPT codes describing anesthesia services or services bundled into anesthesia should not be billed alongside the surgical procedure requiring that anesthesia.

Incorrect or Missing Modifiers

This is the most operationally preventable cause of bundled denials. When two services are genuinely distinct and separately reportable, the correct modifier must be appended to the secondary code to signal the payer that an override applies.

Without a valid modifier, the automated edit fires and the code is denied — even when the services were clinically separate.

Billing E/M Services Without Modifier 25

When a provider performs both an Evaluation and Management (E/M) visit and a procedure on the same date, the E/M service may be considered bundled into the procedure’s pre-operative work unless Modifier 25 is appended. Modifier 25 certifies that the E/M was a separately identifiable service — not just routine pre/post-procedure assessment.

Failure to Recognize Mutually Exclusive Code Pairs

Some code pairs are considered mutually exclusive — meaning it is medically impossible or illogical for both to be performed appropriately during the same encounter. These are listed in the NCCI PTP edit tables. Billing both codes without understanding this relationship results in an automatic denial of the secondary code.

Key Denial Codes Associated with Bundling

CO-97 is the primary bundling denial code. It appears on the Explanation of Benefits (EOB) or Electronic Remittance Advice (ERA). It is governed by your payer’s participation agreement, meaning the write-off is mandatory unless a legitimate appeal overturns the denial.

Modifiers That Override Bundling Rules

Modifier 59 

Modifier 59 is the most commonly used tool to override NCCI bundling edits when services are genuinely distinct. It signals to the payer that the procedures involved are separate and independent, performed at different anatomic sites, during different sessions, or addressing different conditions.

Appropriate use cases per CHB Medical Billing (December 2025):

• Services are performed in separate sessions on the same day
• Procedures on different parts of the body
• Distinct injuries or conditions treated in the same encounter
• Multiple excisions at different incision sites

Caution: 

Modifier 59 is widely flagged as a high-risk modifier for audit. CMS has stated that it is the modifier of last resort,  to be used only when no more specific modifier applies. Overuse without documentation triggers Targeted Probe and Educate (TPE) audits.

The X-Modifier Subset (XE, XS, XP, XU)

Introduced by CMS in 2015 and increasingly required by payers in 2026, the X-modifiers provide more specific documentation of why two services are distinct:

• XE – Separate Encounter (different time of day)
• XS – Separate Structure (different organ or anatomic site)
• XP – Separate Practitioner (different provider in the same group)
• XU – Unusual Non-Overlapping Service

Per ProMBS (March 2026), Medicare and many commercial payers now demand greater specificity, and the X-modifiers offer clearer, more defensible documentation than Modifier 59 alone. When applicable, X-modifiers should be the first choice before defaulting to Modifier 59.

Modifier 25

Modifier 25 applies exclusively to E/M codes. It certifies that the office visit performed on the same day as a procedure was a separately identifiable clinical encounter — not just pre-procedure work.

Modifier 51 and Modifier 22

• Modifier 51 (Multiple Procedures) — used when multiple procedures beyond the primary are performed in the same session; it reduces reimbursement by a percentage rather than causing a full bundling denial.
• Modifier 22 (Increased Procedural Services) — used when the work required to perform a service was substantially greater than typically required; does not override bundling but supports documentation for complexity.

How to Appeal a Bundled Denial

Here is the step-by-step process to appeal a bundle denial:

Identify the Exact Edit Pair and Modifier Indicator

Before drafting any appeal, verify the specific NCCI PTP edit pair using the CMS edit tables (available at cms.gov). Confirm:

• Which code is Column One, and which is Column Two
• Whether the Modifier Indicator is 0 or 1
• Whether the denial occurred at the line level or claim level

If the Modifier Indicator is 0, no modifier can override the edit. The claim must be evaluated for incorrect coding, and the denial is likely correct.

Gather Clinical Documentation

For any Modifier Indicator 1 denial that your team believes was legitimately separate, the appeal must be supported by:

• Operative reports clearly documenting separate anatomic sites or distinct medical decision-making
• Progress notes that demonstrate an independently identifiable E/M service (for Modifier 25 scenarios)
• Separate encounter notes for different sessions on the same date of service

Documentation specificity is the difference between a successful appeal and a second denial.

Apply the Correct Modifier and Resubmit or File a Formal Appeal

Depending on the payer and timeline:

• Corrected claim resubmission — if the denial was due to a missing modifier and the timely filing window has not expired. Add the appropriate modifier and resubmit.
• Formal appeal — if the modifier was correctly applied but the payer still denied, or if the resubmission window has passed.

Track and Escalate

The standard appeals timelines are as follows:

• Medicare: 12-month timely filing; appeal within 120 days of denial
• Medicaid: 90–365 days (state-dependent)
• Commercial payers: 90–180 days

Frequently Asked Questions on Bundled Denial

Can I bill the patient for a CO-97 bundled denial?

No. CO-97 is a Contractual Obligation denial, meaning the financial responsibility falls on the provider under the terms of your payer agreement, not the patient. Billing patients for CO adjustments violates your contract and can lead to audit triggers and termination from payer networks.

Can an ABN protect against bundling denials for Medicare patients?

No. Per CMS NCCI FAQ guidance, an Advance Beneficiary Notice (ABN) is inappropriate for NCCI bundling or MUE denials. These are coding denials, not medical necessity denials, and ABNs do not shift liability to the beneficiary in these situations.

How do I know if an NCCI edit can be overridden with a modifier?

Check the PTP edit table for the code pair on the CMS NCCI webpage. Each edit carries a Modifier Indicator — 0 means no modifier can override, 1 means a modifier may apply if services were genuinely distinct. The NCCI Policy Manual (effective January 1, 2026) explains the rationale for each edit category.

What’s the difference between a bundling denial and an unbundling audit?

A bundling denial is the payer’s action, refusing to reimburse a service already included in another payment separately. Unbundling is a provider-side billing practice where comprehensive codes are split into components to inflate charges. Unbundling CMS or MAC flags can trigger a formal compliance investigation and False Claims Act exposure.

How often should we audit our bundled denial patterns?

Monthly at a minimum. Per the American Medical Association’s claims recovery data and industry RCM guidance, recurring denial patterns by CPT code pair and provider almost always reflect a correctable upstream issue. Monthly denial trending reports allow teams to identify and close those gaps before they become systemic losses.

Conclusion

Bundled denial is not a back-office nuisance. It is a measurable, trackable, and largely preventable revenue drain that compounds every quarter your team does not actively address it.

The rules governing bundling are updated quarterly by CMS and continuously by commercial payers.  Without a structured, proactive approach to bundling compliance, practices leave thousands, often tens of thousands of dollars in write-offs every year.

The solution is threefold: accurate coding aligned with current NCCI edits, complete provider documentation that supports every modifier used, and a denial management workflow that catches CO-97 patterns before they become habits.

Ready to Stop Bundled Denials From Draining Your Practice’s Revenue? NYC Medical Billing specializes in denial prevention, NCCI compliance, and full-cycle revenue recovery for medical practices across New York City and beyond. 

Our certified billing specialists stay current with every quarterly NCCI update. Contact us today for a free denial audit and discover exactly how much bundled denials are costing your practice.