Modifier AA is a HCPCS Level II anesthesia modifier used to indicate that an anesthesia service was personally performed by an anesthesiologist. It is one of the most frequently used anesthesia modifiers in physician billing and is recognized by Medicare, Medicaid, and most commercial insurance carriers.

Anesthesia services are billed differently from Evaluation and Management (E/M), surgery, radiology, and laboratory services. Reimbursement is generally calculated using:

Base Units
Time Units
Conversion Factor

Modifier AA tells the payer that the anesthesiologist personally provided the entire anesthesia service, including the pre-anesthesia evaluation, induction, continuous monitoring during the procedure, emergence, and post-anesthesia care. It also confirms that the anesthesiologist was not medically directing or medically supervising another anesthesia provider during the service. Medicare recognizes Modifier AA for personally performed anesthesia services under the Medicare Physician Fee Schedule (MPFS). (CMS Medicare Claims Processing Manual, Chapter 12)

Modifier

Modifier Name

Anesthesia Services Performed Personally by Anesthesiologist

Plain English Explanation

Modifier AA tells the payer:

“The anesthesiologist personally performed the entire anesthesia service without medical direction or medical supervision of another anesthesia provider.”

Purpose of Modifier AA

Modifier AA is used to:

Identify anesthesia personally performed by an anesthesiologist.
Distinguish personally performed anesthesia from medically directed or medically supervised services.
Support correct Medicare anesthesia reimbursement.
Prevent duplicate billing between anesthesiologists and Certified Registered Nurse Anesthetists (CRNAs).
Ensure accurate reporting of anesthesia provider responsibility.

Understanding Modifier AA

An anesthesiologist billing with Modifier AA is responsible for the entire anesthesia care provided to the patient.

This generally includes:

Pre-anesthesia assessment
Review of medical history
Physical examination
Development of the anesthesia plan
Administration of anesthesia
Continuous physiologic monitoring
Airway management
Intraoperative anesthesia care
Emergence from anesthesia
Immediate post-anesthesia evaluation

No portion of the anesthesia service is reported as medically directed or medically supervised by another anesthesia professional.

When to Use Modifier AA

Modifier AA is appropriate when:

An anesthesiologist personally performs the anesthesia service.
No CRNA or Anesthesiologist Assistant (AA-C) performs the anesthesia under medical direction.
The anesthesiologist remains responsible for the patient throughout the anesthesia service.
The anesthesia CPT® code is reported by the anesthesiologist who personally furnished the service.

Common Examples

✔ General anesthesia for appendectomy personally performed by an anesthesiologist.

✔ Spinal anesthesia administered solely by an anesthesiologist.

✔ Epidural anesthesia personally managed by an anesthesiologist.

✔ Monitored anesthesia care (MAC) personally provided by an anesthesiologist when supported by the appropriate anesthesia modifier(s) and payer policy.

When NOT to Use Modifier AA

Do not use Modifier AA when:

The anesthesiologist medically directs one or more CRNAs (use the appropriate medical direction modifier such as QK or QY, depending on the circumstances).
The anesthesiologist medically supervises more than four concurrent anesthesia procedures (Modifier AD may apply).
A CRNA independently performs the anesthesia service without medical direction (Modifier QZ).
A CRNA performs the anesthesia under medical direction (Modifier QX).

Medicare Rules

Under Medicare:

Modifier AA identifies anesthesia services personally performed by an anesthesiologist.
Payment is based on the applicable base units, time units, and the annual Medicare anesthesia conversion factor.
The anesthesiologist must personally perform all required components of the anesthesia service.
The anesthesia record must support continuous involvement throughout the case.
The anesthesia start and stop times must be accurately documented.
Documentation must demonstrate compliance with Medicare anesthesia billing requirements.

Commercial Insurance Rules

Most commercial insurers recognize Modifier AA and generally follow Medicare anesthesia billing principles.

Many commercial payers:

Require documentation supporting personally performed anesthesia.
Review anesthesia records during audits.
Verify anesthesia start and stop times.
Require the appropriate anesthesia CPT® code and diagnosis.
May have payer-specific requirements for medical direction or concurrency.

Always review payer-specific anesthesia policies before claim submission.

Documentation Requirements

Documentation should include:

Pre-anesthesia evaluation.
Patient history and physical assessment.
ASA Physical Status classification.
Planned anesthesia technique.
Signed informed consent (when applicable).
Anesthesia start time.
Anesthesia stop time.
Continuous intraoperative monitoring.
Drugs and anesthetic agents administered.
Airway management documentation.
Post-anesthesia evaluation.
Anesthesiologist’s signature.

Real Billing Examples

Example 1 – General Anesthesia

An anesthesiologist personally administers general anesthesia for a laparoscopic cholecystectomy from induction through recovery.

Billing

Appropriate anesthesia CPT® code
Modifier AA

Modifier AA is appropriate because the anesthesiologist personally performed the complete anesthesia service.

Example 2 – Total Knee Replacement

A patient undergoes total knee arthroplasty.

The anesthesiologist personally performs spinal anesthesia without CRNA involvement.

Billing

Appropriate anesthesia CPT® code
Modifier AA

Example 3 – Colonoscopy

An anesthesiologist personally provides monitored anesthesia care (MAC) for a high-risk patient during a colonoscopy.

When payer policy supports it, the anesthesia CPT® code is billed with Modifier AA (and any additional required modifier, such as QS for MAC, if applicable).

Example 4 – Incorrect Use

A CRNA performs the anesthesia while the anesthesiologist medically directs two concurrent cases.

The anesthesiologist bills:

Anesthesia CPT® code
Modifier AA

This is incorrect because the anesthesiologist did not personally perform the anesthesia service. The appropriate medical direction modifier should be reported instead.

CMS-1500 Claim Example

Field	Example
CPT® Code	Appropriate anesthesia CPT® code (e.g., 00840)
Modifier	AA
Diagnosis Pointer	Appropriate ICD-10-CM diagnosis
Units	Time units as calculated
Charges	Based on base units + time units

Common Denial Reasons

Incorrect anesthesia modifier.
Medical direction modifier should have been reported instead of AA.
Missing anesthesia record.
Missing anesthesia time.
Incomplete documentation.
Duplicate billing by CRNA and anesthesiologist.
Invalid anesthesia CPT® code.

How to Correct the Denial

Review the EOB or ERA.
Verify that the anesthesiologist personally performed the service.
Confirm no medical direction occurred.
Review anesthesia start and stop times.
Submit the complete anesthesia record if requested.
Correct the modifier and resubmit or appeal with supporting documentation.

Coding Tips

Use Modifier AA only when the anesthesiologist personally performs the anesthesia service.
Verify that no CRNA medical direction modifier is applicable.
Accurately document anesthesia start and stop times.
Ensure the anesthesia record supports continuous physician involvement.
Follow Medicare and payer-specific concurrency rules.

Modifier AA vs Modifier QK

Modifier	Description
AA	Personally performed anesthesia by an anesthesiologist.
QK	Medical direction of two, three, or four concurrent anesthesia procedures.

Modifier AA vs Modifier QY

Modifier	Description
AA	Personally performed anesthesia.
QY	Medical direction of one CRNA by an anesthesiologist.

Modifier AA vs Modifier QX

Modifier	Description
AA	Personally performed by an anesthesiologist.
QX	CRNA service furnished with medical direction by a physician.

Modifier AA vs Modifier QZ

Modifier	Description
AA	Personally performed by an anesthesiologist.
QZ	CRNA service without medical direction by a physician.

Frequently Asked Questions (FAQs)

Q1. What does Modifier AA mean?

Answer: Modifier AA indicates that the anesthesiologist personally performed the entire anesthesia service without medical direction or medical supervision of another anesthesia provider.

Q2. Can Modifier AA be used when a CRNA is involved?

Answer: Generally, no. If a CRNA furnishes the anesthesia service under medical direction or independently, the appropriate anesthesia modifiers (such as QX, QY, QK, AD, or QZ) should be reported based on the circumstances.

Q3. How is reimbursement calculated for Modifier AA?

Answer: Medicare anesthesia reimbursement is generally based on the sum of base units and time units multiplied by the applicable anesthesia conversion factor under the Medicare Physician Fee Schedule.

Q4. Is Modifier AA recognized by commercial insurance?

Answer: Yes. Most commercial insurers recognize Modifier AA, although documentation and reimbursement requirements may vary.

AR Caller Tips

When following up on a denied Modifier AA claim:

Verify that the anesthesia service was personally performed.
Confirm that no medical direction modifier should have been used.
Review anesthesia start and stop times.
Request the denial reason and applicable payer policy.
Submit the anesthesia record if requested.
Record the payer representative’s name, reference number, and appeal instructions.

Interview Questions

Question 1

What is Modifier AA?

Answer: Modifier AA identifies anesthesia services personally performed by an anesthesiologist.

Question 2

When should Modifier AA be reported?

Answer: It should be reported when the anesthesiologist personally performs the complete anesthesia service without medically directing or supervising another anesthesia provider.

Question 3

What is the difference between Modifier AA and Modifier QK?

Answer: Modifier AA represents personally performed anesthesia, whereas Modifier QK represents medical direction of two, three, or four concurrent anesthesia procedures.

Practice Scenario

Scenario

An anesthesiologist performs general anesthesia for an open inguinal hernia repair. The physician completes the pre-anesthesia evaluation, administers anesthesia, continuously monitors the patient throughout surgery, manages emergence, and performs the post-anesthesia assessment. No CRNA or anesthesiologist assistant participates in the case.

Question

Which modifier should be reported?

Answer

Report the appropriate anesthesia CPT® code with Modifier AA, because the anesthesiologist personally performed the entire anesthesia service.

Related Modifiers

AD – Medical Supervision by a Physician: More Than Four Concurrent Anesthesia Procedures
QK – Medical Direction of Two, Three, or Four Concurrent Anesthesia Procedures
QX – CRNA Service with Medical Direction by a Physician
QY – Medical Direction of One CRNA by an Anesthesiologist
QZ – CRNA Service Without Medical Direction by a Physician
QS – Monitored Anesthesia Care (MAC)

Common Billing Mistakes

Reporting Modifier AA when the anesthesiologist medically directed a CRNA.
Billing Modifier AA with incorrect anesthesia time.
Missing the signed anesthesia record.
Using an incorrect anesthesia CPT® code.
Failing to follow Medicare concurrency rules.

Key Takeaways

Modifier AA identifies anesthesia services personally performed by an anesthesiologist.
It should be used only when the anesthesiologist furnishes the entire anesthesia service.
Do not use Modifier AA for medically directed or medically supervised anesthesia cases.
Accurate anesthesia records, time documentation, and compliance with Medicare billing rules are essential.
Correct application of Modifier AA supports accurate reimbursement and reduces claim denials.

References

CMS Medicare Claims Processing Manual, Chapter 12 – Physicians/Nonphysician Practitioners (Anesthesia Services).
CMS Medicare Physician Fee Schedule (MPFS) – Anesthesia Payment Policies.
Medicare Administrative Contractor (MAC) anesthesia billing guidance.
AMA CPT® Professional Edition (licensed codebook).
ASA Relative Value Guide® (American Society of Anesthesiologists), where applicable.

Conclusion

Modifier AA is a foundational anesthesia modifier that identifies services personally performed by an anesthesiologist. Correct reporting requires understanding Medicare anesthesia payment methodology, documenting the complete anesthesia record, accurately recording anesthesia time, and distinguishing personally performed services from medically directed or supervised anesthesia. Proper use of Modifier AA promotes compliant billing, accurate reimbursement, and fewer claim denials.

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 anesthesia billing principles, and general medical coding practices. It is not an official publication of the American Medical Association (AMA), the American Society of Anesthesiologists (ASA), 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 Administrative Contractor (MAC) guidance, ASA publications, and payer-specific billing policies before coding, billing, or submitting claims.