Modifier GC is a HCPCS Level II modifier used to indicate that a service was performed in part by a resident under the direction of a teaching physician. It is primarily used by teaching hospitals, academic medical centers, and residency training programs when submitting claims to Medicare and other payers that recognize teaching physician billing rules.

Modifier GC does not change the CPT® code itself. Instead, it informs the payer that the billed service involved a resident physician and that the teaching physician met the applicable supervision and documentation requirements established by the Centers for Medicare & Medicaid Services (CMS).

Correct use of Modifier GC is essential for compliance with Medicare’s Teaching Physician Rules, proper reimbursement, and successful audit outcomes.

Modifier

Modifier Name

This Service Has Been Performed in Part by a Resident Under the Direction of a Teaching Physician

Plain English Explanation

Modifier GC tells the payer:

“A resident physician participated in providing this service, and the teaching physician supervised the resident and met Medicare teaching physician requirements.”

Purpose of Modifier GC

Modifier GC is used to:

Identify services involving resident physicians.
Indicate compliance with Medicare Teaching Physician Rules.
Support appropriate reimbursement for teaching hospitals.
Differentiate resident services from services personally performed by physicians.
Improve billing accuracy and audit compliance.

Understanding Modifier GC

Teaching hospitals use resident physicians to provide patient care as part of graduate medical education.

When billing Medicare:

A resident may perform part or all of a service.
The teaching physician must provide the required level of supervision.
The teaching physician must document their participation in accordance with CMS rules.
Modifier GC is appended to the applicable CPT® or HCPCS code when required by Medicare billing instructions.

Modifier GC does not indicate that the resident billed independently. The claim is submitted under the teaching physician when Medicare requirements are satisfied.

When to Use Modifier GC

Modifier GC is appropriate when:

A resident participates in the service.
A teaching physician supervises the resident.
CMS Teaching Physician Rules are met.
The teaching physician documents the required participation.
The service is billable under Medicare teaching physician guidelines.

Common Examples

✔ Office Evaluation and Management (E/M) visit performed with resident participation.

✔ Surgical procedure involving a resident and teaching surgeon.

✔ Endoscopy performed by a resident under teaching physician supervision.

✔ Minor procedure involving resident participation.

When NOT to Use Modifier GC

Do not use Modifier GC when:

The physician personally performs the service without resident involvement.
The resident performs a service that is not billable under Medicare teaching physician rules.
The service qualifies under the Primary Care Exception, where Modifier GE may apply instead.
Required teaching physician supervision is not provided.
Documentation requirements are not met.

Medicare Rules

Under Medicare:

Modifier GC is used for services performed in part by a resident under the direction of a teaching physician.
The teaching physician must satisfy applicable CMS supervision requirements.
The teaching physician must document their participation in the medical record.
Reimbursement is made to the teaching physician or eligible entity when billing requirements are met.
Documentation must support both resident participation and teaching physician involvement.

Always refer to the current CMS Medicare Claims Processing Manual and Medicare Administrative Contractor (MAC) guidance for the latest teaching physician policies.

Commercial Insurance Rules

Commercial payer policies vary.

Many commercial insurers:

Recognize teaching physician billing.
May not require Modifier GC.
May instead rely on documentation requirements.
Follow payer-specific reimbursement policies.

Always verify payer-specific billing requirements before claim submission.

Documentation Requirements

Documentation should include:

Resident’s clinical documentation.
Teaching physician’s note.
Evidence of supervision.
Confirmation of physician participation.
Date and time of service, where required.
Procedure note (if applicable).
Medical necessity.
Physician signature.

Real Billing Examples

Example 1 – Office Visit

A resident performs an established patient office visit.

The teaching physician evaluates the patient, confirms the findings, participates in the management plan, and documents the required supervision.

Billing

CPT® 99213
Modifier GC

Example 2 – Colonoscopy

A resident performs part of a colonoscopy while the teaching physician is present during the critical portions of the procedure and documents the required participation.

Billing

Appropriate colonoscopy CPT® code
Modifier GC

Example 3 – Surgical Procedure

A surgical resident assists with an appendectomy under the supervision of the teaching surgeon.

The teaching surgeon documents their presence during the critical portions of the procedure.

Billing

Appropriate surgical CPT® code
Modifier GC

Example 4 – Incorrect Use

A resident independently evaluates a patient without the required teaching physician supervision.

Billing with Modifier GC is incorrect because Medicare teaching physician requirements were not satisfied.

CMS-1500 Claim Example

Field	Example
CPT® Code	99213
Modifier	GC
Diagnosis Pointer	Appropriate ICD-10-CM diagnosis
Provider	Teaching Physician

Common Denial Reasons

Missing teaching physician documentation.
Resident participation not documented.
Teaching physician not present when required.
Incorrect modifier selection.
Service billed under the wrong provider.
Missing signatures.
Incomplete medical record.

How to Correct the Denial

Review the EOB or ERA.
Verify teaching physician documentation.
Confirm resident participation.
Ensure supervision requirements were met.
Submit corrected documentation if appropriate.
Appeal with supporting records when necessary.

Coding Tips

Understand the difference between Modifier GC and Modifier GE.
Ensure teaching physician documentation is complete.
Verify CMS supervision requirements before billing.
Maintain complete resident and physician records.
Review MAC guidance for local billing instructions.

Modifier GC vs Modifier GE

Modifier	Description
GC	Service performed in part by a resident under the direction of a teaching physician.
GE	Service performed by a resident without the presence of a teaching physician under the Medicare Primary Care Exception.

Modifier GC vs Modifier 25

Modifier	Description
GC	Identifies resident participation under teaching physician rules.
25	Identifies a significant, separately identifiable E/M service on the same day as another procedure.

Modifier GC vs Modifier 59

Modifier	Description
GC	Teaching physician modifier.
59	Distinct procedural service modifier.

Frequently Asked Questions (FAQs)

Q1. What does Modifier GC mean?

Answer: Modifier GC indicates that a service was performed in part by a resident under the direction of a teaching physician.

Q2. Who reports Modifier GC?

Answer: Modifier GC is reported on claims submitted by the teaching physician or eligible teaching institution when Medicare teaching physician requirements are met.

Q3. Is Modifier GC used only for Medicare?

Answer: It is primarily associated with Medicare teaching physician billing, although some other payers may recognize it. Always verify payer-specific requirements.

Q4. Does Modifier GC affect reimbursement?

Answer: Modifier GC itself does not change the payment calculation, but it indicates that the service meets Medicare teaching physician billing requirements for reimbursement.

AR Caller Tips

When following up on a denied Modifier GC claim:

Verify teaching physician documentation.
Confirm resident participation.
Check physician signatures.
Review Medicare teaching physician requirements.
Request the payer’s denial reason.
Record the payer representative’s name, reference number, and appeal instructions.

Interview Questions

Question 1

What is Modifier GC?

Answer: Modifier GC identifies services performed in part by a resident under the direction of a teaching physician.

Question 2

What is the difference between Modifier GC and Modifier GE?

Answer: Modifier GC applies when a teaching physician supervises the resident according to Medicare teaching physician rules. Modifier GE is used under the Medicare Primary Care Exception, where certain services may be furnished by residents without the teaching physician being physically present, provided all exception requirements are met.

Question 3

Does Modifier GC change reimbursement?

Answer: No. Modifier GC identifies compliance with Medicare teaching physician requirements. Payment is determined under the applicable Medicare payment methodology for the billed service.

Practice Scenario

Scenario

A resident evaluates an established patient in a teaching hospital clinic. The teaching physician personally sees the patient, confirms the resident’s findings, participates in the treatment plan, documents the required supervision, and signs the medical record.

Question

Which modifier should be reported?

Answer

The applicable CPT® code should be reported with Modifier GC, because the service was performed in part by a resident under the direction of a teaching physician and the Medicare teaching physician requirements were met.

Related Modifiers

GE – Service Performed by a Resident Without the Presence of a Teaching Physician Under the Primary Care Exception
25 – Significant, Separately Identifiable Evaluation and Management Service
59 – Distinct Procedural Service

Common Billing Mistakes

Using Modifier GC when no resident participated.
Missing teaching physician documentation.
Confusing GC with GE.
Billing under the resident instead of the teaching physician when inappropriate.
Missing required physician signatures.
Failing to meet CMS supervision requirements.

Key Takeaways

Modifier GC identifies services performed in part by a resident under the direction of a teaching physician.
It is primarily used in teaching hospitals and academic medical centers.
Medicare requires compliance with Teaching Physician Rules and complete documentation.
Modifier GC generally does not change payment but supports compliant billing.
Accurate supervision and documentation help reduce denials and audit risk.

References

CMS Medicare Claims Processing Manual, Chapter 12 – Physicians/Nonphysician Practitioners (Teaching Physician Services).
CMS Internet-Only Manual (IOM) Publication 100-04 – Medicare Claims Processing Manual.
Medicare Learning Network (MLN) – Teaching Physician Guidelines.
Medicare Administrative Contractor (MAC) teaching physician billing guidance.
AMA CPT® Professional Edition (licensed codebook).

Conclusion

Modifier GC is an essential teaching physician modifier that identifies services performed by residents under the supervision of teaching physicians. Proper use requires adherence to CMS Teaching Physician Rules, accurate documentation of physician participation, and compliance with Medicare billing requirements. Correct reporting of Modifier GC helps ensure accurate reimbursement, regulatory compliance, and successful audit outcomes.

Educational Disclaimer

This article was prepared with the assistance of artificial intelligence (AI) for educational and informational purposes. It is based on publicly available CMS guidance, Medicare teaching physician billing principles, and general medical coding practices. It is not an official publication of the American Medical Association (AMA), CMS, or any insurance payer. CPT® is a registered trademark of the American Medical Association. Always consult the latest AMA CPT® codebook, CMS Medicare Claims Processing Manual, Medicare Learning Network (MLN) guidance, Medicare Administrative Contractor (MAC) policies, and payer-specific billing requirements before coding, billing, or submitting claims.