Modifier AA
Anesthesia Services Personally Performed by Anesthesiologist
Learn what Modifier AA means, when to use it, how personally performed anesthesia differs from medical direction and medical supervision, how anesthesia time is reported, common denials, AR follow-up strategies and practical billing examples.
Modifier AA at a Glance
The essential points every anesthesia biller, coder and AR caller should know.
Personally Performed
CMS defines AA as anesthesia services performed personally by an anesthesiologist.
Full Rate
For Medicare’s anesthesia payment methodology, AA identifies a personally performed service rather than a medically directed service.
Anesthesia Time
Medicare calculates anesthesia payment using allowable base units and anesthesia time units with the applicable conversion factor.
Medicare Rule
CMS lists AA among the anesthesia payment modifiers in the Medicare Claims Processing Manual.
What Is Modifier AA?
Understanding personally performed anesthesia services.
Simple Definition
Modifier AA is an anesthesia modifier used to indicate that the anesthesia service was personally performed by the anesthesiologist.
In Medicare billing, AA is one of the payment modifiers used to distinguish a personally performed anesthesia service from services that are medically directed or medically supervised.
CMS’s Medicare Claims Processing Manual specifically defines AA as “anesthesia services performed personally by anesthesiologist.”
Easy Way to Remember
Think:
“AA = Anesthesiologist Alone.”
When the anesthesiologist personally performs the anesthesia service and the Medicare requirements for personally performed billing are met, AA identifies that service.
Do not confuse Modifier AA with the abbreviation “AA” sometimes used for anesthesiologist assistants. In this modifier context, AA is the anesthesia billing modifier.
What Does Modifier AA Represent?
AA identifies the anesthesia service as personally performed by the anesthesiologist.
Anesthesiologist
The service is personally performed by the anesthesiologist.
Patient Care
The anesthesiologist provides the anesthesia service rather than merely directing another qualified individual.
Anesthesia Time
Actual anesthesia time is reported according to applicable Medicare and payer requirements.
Payment Modifier
AA is a payment modifier used to identify the personally performed anesthesia service.
AA vs QK vs QY vs QX vs QZ
Understanding the major Medicare anesthesia payment modifiers.
| Modifier | Meaning | Typical Medicare Context | Who Reports It? |
|---|---|---|---|
| AA | Anesthesia services personally performed by anesthesiologist | Personally performed | Anesthesiologist |
| QK | Medical direction of 2, 3 or 4 concurrent anesthesia procedures involving qualified individuals | Medical direction | Anesthesiologist |
| QY | Medical direction of one CRNA by an anesthesiologist | Physician medical direction | Anesthesiologist |
| QX | CRNA service with medical direction by physician | Medically directed CRNA service | CRNA |
| QZ | CRNA service without medical direction by physician | CRNA without physician medical direction | CRNA |
| AD | Medical supervision by physician; more than 4 concurrent anesthesia procedures | Medical supervision | Physician |
Key Difference
AA is not a medical-direction modifier. It identifies an anesthesia service personally performed by the anesthesiologist. CMS separately lists QK, QY, QX, QZ and AD for other anesthesia arrangements.
Personally Performed vs Medical Direction
This is one of the most important concepts when working anesthesia claims.
Modifier AA — Personally Performed
- Anesthesiologist personally performs the anesthesia service.
- AA identifies the personally performed service.
- The service is not being reported as medical direction of another anesthesia professional.
- Medicare uses the applicable personally performed anesthesia payment methodology.
Medical Direction
- Anesthesiologist medically directs qualified anesthesia professionals.
- Different anesthesia modifiers identify the medical-direction arrangement.
- The physician must satisfy the applicable Medicare medical direction requirements.
- Payment is generally different from personally performed anesthesia.
AR Tip
When an anesthesia claim is denied because of AA, first determine whether the provider actually performed the service personally or whether another anesthesia professional participated. Do not simply replace AA with QK, QY, QX or QZ without verifying the actual clinical arrangement and payer requirements.
How Medicare Calculates Anesthesia Payment
Understanding the basic components helps AR callers troubleshoot payment differences.
Base Units
The anesthesia code has assigned base units used in calculating the allowable amount.
Time Units
Medicare calculates anesthesia time using applicable time-unit rules.
Conversion Factor
The applicable locality-specific anesthesia conversion factor is used in the payment calculation.
Payment Modifier
The anesthesia modifier identifies the applicable payment arrangement.
CMS Formula Concept
CMS describes the Medicare anesthesia payment calculation using the anesthesia base units plus anesthesia time units, multiplied by the applicable locality-specific anesthesia conversion factor, subject to the applicable payment and beneficiary cost-sharing rules.
Anesthesia Time and Modifier AA
Time reporting is critical for anesthesia claim processing.
Medicare Time Concept
For Medicare anesthesia payment, anesthesia time is used to determine anesthesia time units.
CMS describes one anesthesia time unit as 15 minutes for its anesthesia payment methodology.
Therefore, a 60-minute anesthesia service would represent 4 time units under that calculation.
Simple Example
Anesthesia time:
60 minutes ÷ 15 = 4 time units
If the anesthesia code has 5 base units:
5 base units + 4 time units = 9 total units
The actual Medicare payment then depends on the applicable conversion factor and other payment rules.
Important
Do not assume every payer uses identical anesthesia time and rounding rules. For Medicare, verify the current Medicare Claims Processing Manual and applicable payer/MAC requirements.
Modifier AA Practical Examples
Real-world style scenarios for billers and AR callers.
An anesthesiologist personally performs the anesthesia service for a surgical procedure. No CRNA or other anesthesia professional is performing the anesthesia service under the physician’s medical direction.
Anesthesia CPT + AAThe claim may use Modifier AA when the service meets the applicable Medicare and payer requirements.
A CRNA performs the anesthesia service while an anesthesiologist provides medical direction.
NOT AAThe anesthesiologist and CRNA would use the applicable medical-direction modifiers rather than treating the service as personally performed.
An anesthesiologist medically directs multiple concurrent anesthesia procedures involving qualified individuals.
QKThe applicable medical-direction modifier should be determined from the actual circumstances. AA would not describe the physician’s service merely because the anesthesiologist was involved in the cases.
A CRNA performs an anesthesia service without medical direction by a physician.
QZThis is not an AA situation because AA identifies a service personally performed by an anesthesiologist.
An anesthesia claim is submitted with AA, but the payer’s records indicate that another anesthesia professional performed the anesthesia service.
REVIEW AAThe AR caller should verify the actual provider roles, anesthesia record and payer requirements before correcting the claim.
The claim is billed with AA, but the payer’s processed anesthesia time differs from the time documented in the anesthesia record.
TIME REVIEWCompare the claim’s anesthesia time with the medical record and payer processing before requesting a payment review.
Common Modifier AA Denials
Common anesthesia billing problems encountered in AR.
Invalid Modifier
The payer indicates that AA is not appropriate for the submitted service or provider arrangement.
Wrong Anesthesia Modifier
The payer determines that the actual service involved medical direction or supervision rather than personally performed anesthesia.
Provider Role Mismatch
The provider on the claim does not match the provider identified as performing the anesthesia service.
Time Discrepancy
The anesthesia time on the claim does not match the payer’s processed time or documentation.
Documentation Required
The payer requests the anesthesia record or other documentation supporting personally performed anesthesia.
Duplicate Anesthesia
Another anesthesia claim may have already been processed for the same beneficiary, date and procedure.
Incorrect Units
The payer questions the reported anesthesia time units or total units.
Bundling / Coding Edit
The claim may encounter coding edits involving the anesthesia service or related services.
Coverage / Eligibility
The anesthesia service may deny because of coverage, eligibility or benefit limitations unrelated to AA itself.
Modifier AA Denial Decision Workflow
Follow this sequence before correcting or appealing an anesthesia denial.
AR Caller Workflow for Modifier AA Denials
A practical denial-management workflow for anesthesia claims.
Review the ERA / EOB
Identify the exact denial message and affected anesthesia claim line.
Verify the Anesthesia CPT
Confirm the exact anesthesia code submitted.
Verify Modifier AA
Determine whether the service was personally performed by the anesthesiologist.
Verify Provider Role
Confirm whether the anesthesiologist personally performed the case or medically directed another qualified individual.
Review Anesthesia Record
Verify documentation supporting the anesthesia service and reported time.
Verify Time
Compare claim time with the anesthesia record and payer processing.
Check Units
Confirm base units and time units used in the claim.
Check Payer Policy
Review Medicare, MAC, Medicaid or commercial payer requirements applicable to the claim.
Identify Root Cause
Determine whether the problem is modifier, provider role, documentation, time, units, coding or coverage.
Correct or Appeal
Submit the appropriate corrected claim or appeal with supporting documentation.
Document the Follow-Up
Record representative name, reference number, filing deadline and next action.
AR Caller Script for Modifier AA Denial
Questions to ask the payer during an anesthesia modifier denial.
“I’m calling regarding an anesthesia claim submitted with Modifier AA.”
“Could you please provide the exact denial reason and the applicable CARC and RARC codes?”
“Can you confirm whether the denial is specifically related to Modifier AA?”
“Can you confirm whether AA is accepted for this anesthesia code under the member’s plan?”
“Does your system indicate that the anesthesia service was personally performed or medically directed?”
“Is there another anesthesia provider’s claim already processed for this date of service?”
“Are you requesting the anesthesia record to validate personally performed services?”
“Is the denial related to anesthesia time or reported units?”
“If a corrected claim is required, what modifier or claim correction should be submitted?”
“If an appeal is appropriate, what documentation should be attached?”
“May I have the call reference number for our records?”
Modifier AA Documentation Checklist
Information the billing and AR team should verify.
Anesthesia Record
Documentation supporting the anesthesia service.
Performing Provider
Confirm the anesthesiologist who personally performed the service.
Anesthesia Start
Verify the documented start of anesthesia time.
Anesthesia End
Verify when anesthesia care ended according to applicable requirements.
Total Time
Compare documented anesthesia time with the claim.
CPT Code
Verify the anesthesia CPT/HCPCS code.
Modifier
Confirm AA was reported when the actual service supports it.
Medical Direction
Verify that the case was not actually medically directed.
Payer Policy
Review the current payer-specific anesthesia billing requirements.
Common Modifier AA Billing Mistakes
Using AA for Every Anesthesia Claim
AA should not be automatically added to every anesthesia claim. The actual provider arrangement must support personally performed anesthesia.
Confusing AA With QK
QK represents medical direction of two, three or four concurrent anesthesia procedures. It does not represent personally performed anesthesia.
Confusing AA With QY
QY represents medical direction of one CRNA by an anesthesiologist. AA identifies personally performed anesthesia.
Ignoring the Anesthesia Record
The claim should be supported by documentation that matches the billed anesthesia service and time.
Ignoring Time Differences
A mismatch between claim time and documentation can result in payment differences or denials.
Assuming Every Payer Is Identical
Medicare, Medicaid, Medicare Advantage and commercial payers can have different processing and documentation requirements.
Medicare Anesthesia Modifier Reference
A quick reference for the most commonly encountered anesthesia payment modifiers.
| Modifier | Description | Primary Concept | Commonly Reported By |
|---|---|---|---|
| AA | Anesthesia services personally performed by anesthesiologist | Personally performed | Anesthesiologist |
| QK | Medical direction of 2–4 concurrent anesthesia procedures | Medical direction | Anesthesiologist |
| QY | Medical direction of one CRNA | Medical direction | Anesthesiologist |
| QX | CRNA service with medical direction by physician | Medical direction | CRNA |
| QZ | CRNA service without medical direction | CRNA without physician medical direction | CRNA |
| AD | Medical supervision by physician; more than 4 concurrent anesthesia procedures | Medical supervision | Physician |
| QS | Monitored anesthesia care service | Informational MAC modifier | Physician or qualified nonphysician anesthetist |
Remember QS
CMS states that QS identifies monitored anesthesia care for informational purposes. A payment modifier must also be reported. Therefore, QS does not replace the applicable payment modifier.
Modifier AA and Medicare in 2026
Current Medicare resources to verify anesthesia billing.
2026 Anesthesia Data
CMS’s Anesthesiologists Information Center states that the 2026 anesthesia base units are unchanged.
Claims Manual
Medicare Claims Processing Manual Chapter 12 provides anesthesia claims modifier guidance.
NCCI
Review the current Medicare NCCI Policy Manual when evaluating applicable anesthesia coding edits.
Conversion Factor
Medicare anesthesia payment uses the applicable locality-specific anesthesia conversion factor.
Time
Verify actual anesthesia time and applicable Medicare time-unit rules.
MAC Requirements
When a Medicare Administrative Contractor policy applies, verify the current MAC-specific instructions.
CMS 2026 Update
CMS’s Anesthesiologists Information Center currently provides the 2026 anesthesia conversion-factor resources and notes that anesthesia base units are unchanged for CY 2026.
Modifier AA Payment Example
Simplified educational example based on CMS’s anesthesia calculation concept.
Example
Assume:
- Anesthesia base units = 4
- Anesthesia time = 60 minutes
- Time units = 4
- Total units = 8
- AA = personally performed by anesthesiologist
Calculation Concept
Base Units + Time Units
4 + 4 = 8 units
The 8 allowable units are then multiplied by the applicable locality-specific anesthesia conversion factor, subject to Medicare payment rules.
CMS provides a similar illustrative calculation in its Medicare Claims Processing Manual.
Educational Example Only
The actual Medicare allowed amount varies by locality, anesthesia code, applicable conversion factor and claim-specific payment rules. Do not use the sample calculation as a current reimbursement quote.
How to Prevent Modifier AA Denials
Verify Provider
Confirm that the anesthesiologist personally performed the anesthesia service.
Verify Modifier
Use AA only when the actual service arrangement supports it.
Verify Time
Compare claim time with the anesthesia record before submission.
Verify Units
Confirm base units and applicable time units.
Check Payer Policy
Review Medicare, MAC or commercial payer anesthesia requirements.
Audit Denials
Track AA denials by payer, provider, anesthesia code, reason and root cause.
Modifier AA Quick Cheat Sheet
- AA = anesthesia services personally performed by anesthesiologist.
- AA is an anesthesia payment modifier.
- Do not confuse Modifier AA with “anesthesiologist assistant.”
- AA is different from QK and QY medical-direction modifiers.
- QX identifies CRNA service with medical direction by physician.
- QZ identifies CRNA service without medical direction by physician.
- AD identifies medical supervision by a physician for more than four concurrent anesthesia procedures.
- QS identifies monitored anesthesia care for informational purposes and does not replace the payment modifier.
- Verify actual anesthesia time.
- Verify anesthesia base units and applicable payment rules.
- Review the current Medicare Claims Processing Manual.
- Review applicable MAC and payer-specific requirements.
- Maintain supporting anesthesia documentation.
- Document payer calls and denial root causes.
Before You Bill Modifier AA
- Confirm the anesthesia CPT/HCPCS code.
- Confirm the anesthesiologist personally performed the service.
- Confirm no other anesthesia professional performed the service under medical direction.
- Verify anesthesia start and end times.
- Verify total anesthesia time.
- Verify base units.
- Verify applicable time units.
- Confirm Modifier AA is appropriate.
- Review payer-specific anesthesia billing rules.
- Confirm provider enrollment and billing arrangement.
- Confirm documentation is available if requested.
Modifier AA FAQs
What is Modifier AA?
Modifier AA indicates anesthesia services personally performed by an anesthesiologist.
What does AA mean in anesthesia billing?
AA identifies the anesthesia service as personally performed by the anesthesiologist rather than medically directed.
Does Modifier AA mean the anesthesiologist performed the entire anesthesia service?
In the Medicare modifier context, AA identifies anesthesia services personally performed by the anesthesiologist. The actual clinical circumstances and payer requirements should always be verified.
What is the difference between AA and QK?
AA identifies personally performed anesthesia by the anesthesiologist. QK identifies medical direction of two, three or four concurrent anesthesia procedures involving qualified individuals.
What is the difference between AA and QY?
AA represents personally performed anesthesia. QY represents medical direction of one CRNA by an anesthesiologist.
What is the difference between AA and QZ?
AA is for personally performed anesthesia by an anesthesiologist. QZ is for a CRNA service without medical direction by a physician.
Is AA a modifier for an anesthesiologist assistant?
No. In this context, AA is the anesthesia billing modifier meaning anesthesia services personally performed by an anesthesiologist. Anesthesiologist assistants are a separate provider category.
Is Modifier AA used with anesthesia CPT codes?
AA is used with applicable anesthesia services when the service was personally performed by the anesthesiologist and the payer’s rules support the reporting.
How is anesthesia time calculated for Medicare?
Medicare’s anesthesia payment methodology uses anesthesia time units. CMS describes one time unit as 15 minutes for this calculation.
Does AA automatically mean 100% payment?
AA identifies personally performed anesthesia. Medicare’s payment methodology pays the personally performed service differently from medically directed services, but the actual allowed amount depends on the applicable anesthesia code, units, conversion factor and other claim-specific rules.
What documentation supports Modifier AA?
Supporting documentation may include the anesthesia record, provider identification, anesthesia times and other records required by the payer to establish that the service was personally performed.
Can an AR caller appeal an AA denial?
Yes, when the claim accurately represents personally performed anesthesia and the documentation supports the service. Verify the payer’s denial reason and appeal requirements first.
What should I check first for an AA denial?
Start with the ERA/EOB denial reason. Then verify the anesthesia CPT, provider role, AA modifier, anesthesia record, time, units and payer policy.
Is AA used when an anesthesiologist medically directs a CRNA?
No. When an anesthesiologist medically directs a CRNA, the applicable medical-direction modifiers should be used based on the actual circumstances. AA identifies personally performed anesthesia.
Does Modifier AA apply to all insurance companies?
Modifier AA is an established anesthesia modifier, but payer processing requirements can differ. Always verify the specific payer’s current billing policy.
Official CMS References
Use official CMS resources when verifying current Medicare anesthesia billing requirements.
Coding Disclaimer
This page is intended for medical billing, coding and RCM education. Anesthesia coding and payment can depend on the exact CPT code, provider type, clinical circumstances, payer policy, Medicare Administrative Contractor instructions and applicable documentation. Always verify current official guidance before submitting or correcting a claim.
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