Anesthesia Modifiers AA, QK, QX, QY, QZ & AD — Medicare Rules

Which Anesthesia Modifier Do You Use?

Every Medicare anesthesia claim needs a payment modifier that says who gave the anesthesia and how. Physicians use AA, QY, QK or AD. Nurse anesthetists (CRNAs) use QX or QZ, and anesthesiologist assistants use QX. The modifier is not just paperwork. It decides whether the case is paid in full, split 50/50 between the doctor and the CRNA, or cut to three base units.

Modifier	Who reports it	Meaning (CMS)	Medicare payment
AA	Anesthesiologist	Anesthesia services performed personally by the anesthesiologist	Full anesthesia fee schedule amount
QY	Anesthesiologist	Medical direction of one qualified nonphysician anesthetist	50% of the amount for personally performing it
QK	Anesthesiologist	Medical direction of two, three or four concurrent anesthesia procedures	50% of the amount for personally performing it
AD	Anesthesiologist	Medical supervision; more than four concurrent anesthesia procedures	3 base units, plus 1 time unit if present at induction
QX	CRNA or anesthesiologist assistant	Qualified nonphysician anesthetist service with medical direction by a physician	50% of the amount for personally performing it
QZ	CRNA	CRNA service without medical direction by a physician	Full anesthesia fee schedule amount

The pairs have to agree. A physician billing QY or QK means the CRNA on the same case bills QX. A CRNA billing QZ means no physician is claiming medical direction. A QK on one claim and a QZ on the other contradicts itself, and payers deny one or both.

What the Modifier Does to the Money

Take a case with 7 base units and 63 minutes of anesthesia (4.2 time units). Use the 2026 national Medicare anesthesia conversion factor of $20.4975:

How the case was staffed	Claims	Medicare allowable
Anesthesiologist alone	Physician: AA	11.2 units × $20.4975 = $229.57
Anesthesiologist directing one CRNA	Physician: QY · CRNA: QX	$114.79 each (50% / 50%)
Anesthesiologist directing three concurrent rooms	Physician: QK · each CRNA: QX	$114.79 per case to each
Anesthesiologist covering five concurrent rooms	Physician: AD	Physician: 3 base units = $61.49 ($81.99 with the induction time unit)
CRNA with no medical direction	CRNA: QZ	$229.57

These are national amounts, before local adjustment, the 2% sequestration cut and the patient’s coinsurance. Our anesthesia billing calculator runs the same math with your locality’s 2026 conversion factor.

The Seven Medical Direction Requirements

QK and QY only count if the physician does all seven things CMS lists, for every directed case. Miss one and it is not medical direction:

Performs a pre-anesthetic examination and evaluation.

Prescribes the anesthesia plan.

Personally participates in the most demanding procedures in the plan, including induction and emergence where applicable.

Ensures any procedures in the plan that he or she does not perform are performed by a qualified individual.

Monitors the course of anesthesia administration at frequent intervals.

Remains physically present and available for immediate diagnosis and treatment of emergencies.

Provides indicated post-anesthesia care.

The record must show four things: the pre-anesthetic evaluation, the post-anesthesia care, presence for part of the monitoring, and presence for the most demanding steps. In a group practice, one physician can do the evaluation and another the rest. The record just has to name who did what.

Concurrency: QK or AD?

Concurrency counts every overlapping case the physician is directing, not just the Medicare ones. CMS gives this example: an anesthesiologist directing three overlapping cases, two of them non-Medicare patients, is directing three concurrent cases. Two to four concurrent cases is QK. Add a fifth and the cases in that window become AD. The physician’s payment then drops from half the full rate to three base units.

Short breaks do not end medical direction. CMS allows brief tasks like a short emergency nearby, a labor epidural, periodic checks on an obstetric patient, receiving the next patient, or checking patients in recovery. Leaving the operating suite for more than a short time, or spending a long time on an emergency, is not allowed.

When Both AA and QZ Are Allowed

Normally a physician and a CRNA on one case split the payment. CMS allows one exception. In unusual cases where it is medically necessary for both to be fully involved, each is paid in full. The physician bills AA, the CRNA bills QZ, and both must send documentation to support the full fee. Billing AA and QZ together as a habit, without that documentation, is a known audit target.

Informational Modifiers: QS, G8, G9 and GC

QS: monitored anesthesia care (MAC). A physician or a CRNA can use it, but only for information. The claim still needs the real anesthesia time and one of the payment modifiers above. Payer guides usually ask for the payment modifier first and QS after it.

G8: MAC for deep complex, complicated or markedly invasive surgical procedures.

G9: MAC for a patient with a history of a severe cardiopulmonary condition.

GC: a resident did the service under a teaching physician. Report it with a payment modifier, never instead of one.

Physical status modifiers P1 to P6 describe how sick the patient is. Many commercial contracts add units for P3 to P5. Medicare does not pay them, which is why our calculator keeps them separate.

Sources

Modifier definitions, payment rates and the medical direction rules come from the Medicare Claims Processing Manual, Chapter 12 (§50 and §140). Commercial payers and Medicaid plans can price these modifiers differently, so check the payer’s anesthesia policy for non-Medicare claims.

Anesthesia billing calculator, anesthesiology billing services, all modifier guides, and modifier 51 for multiple anesthesia procedures.

Frequently Asked Questions

What is the QZ modifier in anesthesia?

QZ means a CRNA service without medical direction by a physician. The CRNA is paid on the full anesthesia fee schedule amount, capped at what a physician would be allowed for personally performing the service.

What is the difference between QK and QY?

Both mean the anesthesiologist is medically directing CRNAs and is paid 50% of the full amount. QY is medical direction of one CRNA; QK is medical direction of two, three or four concurrent procedures. In both cases the CRNA bills QX.

When do you use the AD modifier?

When the anesthesiologist is supervising more than four concurrent anesthesia procedures, or is performing other services while directing concurrent cases. Medicare then allows only three base units per procedure, plus one time unit if the physician documents being present at induction.

Does Medicare pay for the QS modifier?

QS is informational. It flags monitored anesthesia care, but the claim is paid according to the payment modifier reported with it, such as AA, QK or QZ, and the actual anesthesia time.

Can AA and QZ be billed on the same case?

Only in unusual circumstances when it is medically necessary for both the anesthesiologist and the CRNA to be completely and fully involved. Each is then paid in full, and both must submit documentation supporting it.

Do non-Medicare cases count toward concurrency?

Yes. Concurrency counts every overlapping case the physician is directing, regardless of the patients' insurance. Three overlapping cases are three concurrent cases even if only one patient has Medicare.

Anesthesia Modifiers — AA, QK, QX, QY, QZ and AD