How to Review Add-On Code and Global Period Denials: A Medical Billing Guide

The code is on the claim. The service was performed. So why isn’t it being paid?

Before you start looking for a coding error, pause for a moment. Could the issue be whether the service qualifies for separate payment? That’s where things get tricky. An add-on code and a service billed during a surgical global period may both end up denied, but the reasons behind those denials can be very different.

So, where should you look first? Is the add-on code linked to an eligible primary procedure, or is the service considered part of the surgical package? Getting to the right answer means knowing which billing rule applies before you spend time correcting, resubmitting, or appealing the claim.

And with claim denials continuing to challenge providers, getting that distinction right matters. According to Experian Health’s 2025 State of Claims Survey, 41% of surveyed providers reported claim denial rates of 10% or higher.

So, how do you tell these two denials apart? Let’s uncover what’s behind each one, what to look for, and how to determine whether the claim has a case for separate payment.

What Makes an Add-On Code Different From a Primary Code?

An add-on code is used to report an additional service performed alongside an eligible primary service. The primary code represents the main service or procedure, while the add-on code captures additional work that meets specific reporting requirements.

Unlike a primary code, an add-on code generally cannot be reported on its own. Its use depends on the applicable CPT instructions, the required relationship with the primary code, and the payer’s rules. Simply performing an additional service doesn’t automatically mean it can be billed separately or will be paid.

How Do Primary and Add-On Codes Work Together?

Not every primary code can be reported with every add-on code. The correct combination depends on the specific codes and their reporting instructions, not just on whether both services were performed during the same encounter.

For example, CPT code 99291 reports the initial critical care service, while CPT code 99292 reports additional critical care time when the applicable requirements are met. To report the additional code, the relevant time and coding requirements must be satisfied. Providing more care alone isn’t enough.

For Medicare claims, consult the CMS Medicare Add-on Code Edits and the applicable instructions for the specific add-on code. Because acceptable primary-code relationships can vary by add-on code type, check the relevant CMS guidance and claims-processing contractor requirements where applicable.

Also Read: CPT, ICD-10 and HCPCS Codes Explained (and Why Claims Deny)

Why Can an Add-On Code Be Denied?

An add-on code may be denied because the claim doesn’t meet one or more requirements for reporting or paying the additional service. Instead of changing the code right away, first identify the specific reason for the denial.

1. Check the Add-On Code Denial Reason

Start by reviewing the submitted claim and the payer’s explanation. Then focus on the issue most relevant to the denial:

• Missing primary code: Check whether the required primary service is included on the claim.
• Ineligible code pairing: Verify that the primary code can be reported with the add-on code.
• Reporting requirements not met: Review the applicable CPT or HCPCS instructions to confirm that the code was reported correctly.
• Coding edit or payer restriction: Check the relevant edits and payer policy for restrictions that may affect the code combination.

Keep in mind that having the primary code on the claim doesn’t automatically mean the add-on code meets all reporting and payment requirements.

2. Verify Current Coding Instructions and Payer Rules

Once you have a likely reason for the denial, check the coding instructions and edits that apply to the date of service.

CMS updates Medicare NCCI edit files quarterly, so make sure you use the version that applies to the claim rather than relying on outdated edits. Other payers may have different requirements, so Medicare rules shouldn’t automatically be applied to every claim.

How Should You Resolve an Add-On Code Denial?

The next step depends on what you find during the review.

• If there’s a coding error: Correct the claim when appropriate and in accordance with the applicable billing rules.
• If the code relationship or reporting requirements are unclear: Check the relevant coding instructions or payer policy before making any changes.
• If the claim appears compliant: Compare the denial reason with the applicable requirements and determine whether the supporting evidence warrants further review or an appeal.

Don’t change a code just because the payer denied it. First, confirm which rule is at issue, then decide whether the claim needs correction or whether the denial should be challenged.

What Does a Global Surgery Period Mean for Billing?

A global surgery period helps determine which services are included in a surgical procedure’s payment and which services may be billed separately. Under Medicare, each procedure has a global surgery indicator that explains how the payment rules apply to the procedure and related care.

1. What’s Included in the Surgical Package?

The surgical package may cover several services related to the procedure, including:

• Preoperative care: Certain visits to prepare the patient for surgery.
• Intraoperative services: The routine work involved in performing the procedure.
• Postoperative care: Certain follow-up visits and care during recovery.
• Postsurgical pain management: Pain management services included in the surgical package.
• Routine recovery services: Services such as routine dressing changes and suture removal.

However, not every service provided before or after surgery is automatically included in the surgical package. Whether a service can be billed separately depends on the type of service and the applicable Medicare or other payer guidelines.

For more details, refer to the CMS Global Surgery booklet.

2. Why Do Timing and the Type of Service Matter?

Medicare uses global surgery indicators to show how the global period applies to a procedure. Some common indicators include:

These are general guidelines, so it’s important to check the current CMS Physician Fee Schedule status indicators for the specific procedure and date of service.

The key point is that both timing and the nature of the service matter. A service provided during the global period may be included in the surgical package, but some services may qualify for separate billing if they meet the applicable reporting requirements. For example, routine postoperative care is generally included, while a service that meets Medicare’s criteria for separate reporting may be billed separately.

Understanding the global surgery period helps ensure that services are reported correctly and that billing follows the applicable payer guidelines.

How to Review a Claim Involving a Global Period?

When a claim is denied because of a global surgery period, the first step is to understand why the payer denied it and whether the decision is correct. Reviewing the claim step by step can help you identify the issue and determine what to do next.

Step 1: Check the Procedure and Global Period

Start by confirming the basic details of the claim.

1. Verify the procedure code and date of service. Make sure you’re reviewing the correct procedure and the date associated with the denied service.
2. Check the global surgery indicator. If the claim is billed to Medicare, review the current Physician Fee Schedule and applicable CMS guidance to confirm the correct indicator.
3. Review the service dates. Determine when the denied service occurred in relation to the surgery and whether it falls within the applicable global period.
4. Confirm the payer’s rules. If the claim is covered by a commercial insurer or another payer, check that payer’s specific guidelines rather than automatically applying Medicare rules.

Step 2: Review the Service and Medical Documentation

Once you’ve confirmed the global period, take a closer look at the denied service and the supporting medical records.

• Check what was billed. Does the procedure or service code accurately reflect what was documented in the medical record?
• Understand why the service was performed. Does the documentation clearly explain the purpose of the visit or service?
• Determine whether it can be billed separately. Based on the applicable payer rules, should the service be included in the surgical package, or does it qualify for separate reporting?
• Look for any applicable exceptions. If you believe an exception applies, make sure the documentation meets the specific requirements.
• Compare everything with the denial reason. Does the payer’s explanation match the actual service, documentation, and applicable billing rules?

Step 3: Decide What to Do Next

After reviewing the claim, you should be able to identify the most appropriate next step.

• The denial is correct: The service is included in the global surgery package, and no separate billing exception applies.
• More information is needed: The documentation or coding needs clarification before you can determine whether the denial is appropriate.
• The denial may be incorrect: The documentation and applicable payer rules support separate reporting, so further review or an appeal may be appropriate.

Don’t automatically resubmit or correct a denied claim just because it involves a global surgery period. First, understand why the claim was denied, verify the applicable rules, and review the supporting documentation. Once you identify the actual issue, you can determine the right next step.

Add-On Code Rules vs. Global-Period Rules

Add-on code denials and global-period denials may both affect claim payment, but they involve different billing rules. The key is to understand what caused the denial so you know which rules to check first.

How to Tell Which Rule Applies?

If the denial concerns an add-on code’s primary-code relationship, investigate the code requirements. If it concerns a service performed during a surgical global period, investigate the applicable package rules. If both issues are relevant, review them separately.

A Claim-Review Workflow for These Two Billing Issues

Add-on-code and global-period denials require different checks. Use the relevant checklist to review the applicable requirements and identify what needs further investigation.

When reviewing these denials, understanding the payer's reasoning and checking it against the claim details and supporting evidence are essential. Bill Matters is designed to help analyze denied medical claims, identify gaps in supporting evidence, and prepare appeal drafts for review when further action may be warranted. This can help medical billing companies structure their denial review and determine the appropriate next steps. The findings should still be verified against the applicable CPT instructions, CMS guidance, and payer-specific policies before correcting or appealing a claim.

Add-On Code Checklist

• Required primary code is present.
• Primary/add-on code pairing is permitted.
• Code set and edits match the date of service.
• Applicable reporting instructions are satisfied.
• Findings align with the stated denial reason.

Global Period Checklist

• Procedure code is verified.
• Applicable global indicator is confirmed.
• Service date is checked against the global period.
• Nature and purpose of the service are established.
• Documentation and payer rules are reviewed for separate-reporting eligibility.

What Documentation and Claim Details Should Be Retained?

Retain the records needed to support the billed service, verify the applicable billing rules, and explain the payer’s decision.

• Claim and service details: Keep the submitted claim, relevant claim lines, procedure codes, dates of service, and denial or remittance information.
• Medical documentation: Retain records showing what service was performed and why it was needed.
• Code instructions and edits: Keep the applicable CPT/HCPCS instructions, relevant add-on-code edits, and global surgery guidance for the date of service.
• Payer policies and decisions: Retain the policy used to review the claim, the denial reason, and any related correspondence or clarification.
• Review rationale and calculations: Document why the coding decision was made and keep any relevant time, unit, or other calculations.

Follow the applicable record-retention requirements and your organization’s policies. Keeping these records organized makes it easier to trace the claim and understand the review decision.

The Bigger Opportunity Is Preventing Repeat Denials

Resolving a denied claim is important, but understanding why the same denials keep happening can make an even bigger difference. Recurring add-on-code or global-period denials may point to issues with coding practices, documentation, payer requirements, or internal review processes.

The financial impact of denials goes beyond individual claims. The American Hospital Association reports that hospitals spent nearly $18 billion in 2025 overturning claim denials alone. While this figure covers denials broadly, not just add-on-code or global-period issues, it highlights how much time and money can go into challenging payment decisions. By tracking denial reasons and appeal outcomes, billing teams can spot recurring patterns, address preventable errors, and focus on claims where the evidence supports further action.

Ultimately, effective denial management isn't about appealing every rejected claim. It's about knowing which claims are worth pursuing, making sure the documentation and applicable rules support the decision, and using what you learn from recurring denials to improve the billing process.