Anesthesia Medical Direction Modifiers: QZ, QK, QY

Every Medicare anesthesia claim carries one payment modifier, and that modifier is not a description of the case. It is an assertion about who did the work and what the anesthesiologist personally performed. Choose QK and you are telling Medicare that a physician satisfied seven specific obligations in each of up to four overlapping rooms. Choose QZ and you are telling Medicare that no physician medically directed the case at all. Auditors read those assertions literally, and the medical record either supports them or it does not.

This guide is about the decision, not the code list. It walks the question that actually determines the modifier — who performed the case, and what did the supervising anesthesiologist actually do? — and the concurrency rules that constrain the answer. Every requirement, percentage and threshold below is drawn from the Medicare Claims Processing Manual (Pub. 100-04), Chapter 12, §50 and §§140.3–140.5.

The decision in one pass

Work through these questions in order. The first one that fits gives you the modifier.

Did the anesthesiologist personally perform the entire case alone? → AA, paid at the personally performed rate.
Was there no physician medical direction at all, with a CRNA running the case? → QZ from the CRNA. No physician modifier, because no physician service is being billed.
Did an anesthesiologist medically direct exactly one qualified nonphysician anesthetist? → QY from the physician and QX from the CRNA or anesthesiologist assistant.
Did an anesthesiologist medically direct two, three or four concurrent cases? → QK from the physician and QX from each nonphysician anesthetist.
Were there more than four concurrent procedures, or was the physician performing other services while directing? → AD, medical supervision, which is not medical direction and is not paid like it.

Notice what the ladder does not ask about: the difficulty of the surgery, the patient’s comorbidities, or how long the case ran. Those affect base units, time units and physical status reporting. They do not affect which payment modifier applies.

The six payment modifiers, as CMS defines them

Modifier	CMS definition (Pub. 100-04, Ch. 12, §50)	Who reports it
AA	Anesthesia services performed personally by the anesthesiologist	Physician
AD	Medical supervision by a physician; more than 4 concurrent anesthesia procedures	Physician
QK	Medical direction of two, three or four concurrent anesthesia procedures involving qualified individuals	Physician
QY	Medical direction of one qualified nonphysician anesthetist by an anesthesiologist	Physician
QX	Qualified nonphysician anesthetist service: with medical direction by a physician	CRNA or AA
QZ	CRNA service: without medical direction by a physician	CRNA only

Two modifiers are frequently mistaken for payment modifiers and are not. QS (monitored anesthesia care) is, in CMS’s words, “for informational purposes” — the manual is explicit that providers “must report actual anesthesia time and one of the payment modifiers on the claim.” G8 and G9 describe MAC for deep, complex or markedly invasive procedures and for patients with a history of severe cardiopulmonary conditions. None of the three can stand alone. Similarly, GC flags resident involvement under a teaching physician and, per the manual’s note, “one of the payment modifiers must be used in conjunction with the GC modifier.”

One structural detail matters for claim assembly: the payment modifier goes in the first modifier field. If QS also applies, it goes second.

What medical direction actually requires

This is the part that decides audits. Medical direction is not a staffing ratio and not a scheduling arrangement. CMS pays at the medically directed rate only if the physician medically directs qualified individuals in two, three or four concurrent cases and performs all seven of the following activities:

Performs a pre-anesthetic examination and evaluation
Prescribes the anesthesia plan
Personally participates in the most demanding procedures in the anesthesia plan, including, if applicable, induction and emergence
Ensures that any procedures in the anesthesia 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

These are conjunctive. Six out of seven is not medical direction.

CMS then imposes a separate documentation obligation on four of them. The physician “must document in the medical record that he or she performed the pre-anesthetic examination and evaluation.” Physicians “must also document that they provided indicated post-anesthesia care, were present during some portion of the anesthesia monitoring, and were present during the most demanding procedures in the anesthesia plan, including induction and emergence, where indicated.”

That is the audit target. A record that establishes the physician was assigned to the room proves nothing. The four documented elements — pre-anesthetic evaluation, presence during monitoring, presence at induction and emergence, post-anesthesia care — are what a reviewer looks for, and their absence converts a QK claim into an overpayment.

The group practice split

The seven steps do not have to be performed by the same physician. If anesthesiologists are in a group practice, one member may provide the pre-anesthesia examination and evaluation while another fulfills the remaining criteria; one member may provide post-anesthesia care while another furnishes the other component parts. The condition is documentary: “the medical record must indicate that the services were furnished by physicians and identify the physicians who furnished them.” Unattributed group documentation defeats the exception.

Concurrency: what counts, and what does not

Concurrency is the constraint that turns a compliant QK into an AD. CMS defines it as “the maximum number of procedures that the physician is medically directing within the context of a single procedure and whether these other procedures overlap each other.”

The trap is payer mix. Concurrency “is not dependent on each of the cases involving a Medicare patient.” CMS gives the example directly: if an anesthesiologist medically directs three concurrent procedures, two involving non-Medicare patients and one a Medicare patient, “this represents three concurrent cases.” A group that counts only its Medicare rooms will systematically under-count concurrency and bill QK on cases that were, in fact, supervision.

Activities that do not break medical direction

A physician furnishing medically directed services “cannot ordinarily be involved in furnishing additional services to other patients.” CMS then carves out a specific list of activities that do not substantially diminish the physician’s scope of control:

Addressing an emergency of short duration in the immediate area
Administering an epidural or caudal anesthetic to ease labor pain
Periodic (rather than continuous) monitoring of an obstetrical patient
Receiving patients entering the operating suite for the next surgery
Checking or discharging patients in the recovery room
Handling scheduling matters

The boundary is drawn immediately afterward. If the physician “leaves the immediate area of the operating suite for other than short durations or devotes extensive time to an emergency case or is otherwise not available to respond to the immediate needs of the surgical patients,” the requirements are not met and the MAC may not pay under the fee schedule.

Residents and student nurse anesthetists

The concurrency rules treat these two groups differently, and the difference is easy to get backwards. For student nurse anesthetists, the medically directed requirements apply if the physician directs two concurrent cases each involving a student nurse anesthetist, or one such case and another involving a qualified individual (CRNA, anesthesiologist assistant, intern or resident). For residents, the medically directed requirements expressly do not apply to a single resident case concurrent to another case paid at the medically directed rate, or to two concurrent resident cases — those route to the personally performed rate under the teaching physician rules instead.

How the money follows the modifier

Anesthesia payment is not RVU-based. The fee schedule amount is built from allowable base units plus time units, multiplied by a locality-specific anesthesia conversion factor. Base units come from the annually released HCPCS file; CMS publishes the conversion factor annually. Time units are computed by dividing reported anesthesia time by 15 minutes, rounded to one decimal place, and are not recognized for CPT 01996. Against that base, the modifier sets the split:

Personally performed (AA) — full base units plus one time unit per 15 minutes.
Medically directed (QK/QY + QX) — the physician is paid “50 percent of the allowance for the service performed by the physician alone.” For a single medically directed procedure, the manual states the payment amount for each of the physician and the nonphysician anesthetist “is 50 percent of the allowance otherwise recognized had the service been furnished by the anesthesiologist alone.” The 50/50 split is the defining economic feature of medical direction.
Medically supervised (AD) — the MAC “may allow only three base units per procedure.” One additional time unit may be recognized “if the physician can document he or she was present at induction.” This is the cliff: crossing from four concurrent cases to five does not reduce payment proportionally, it collapses the physician’s payment to three base units per case.
Non-medically directed CRNA (QZ) — paid on the conversion factor times base plus time units, with the constraint that the locality-adjusted conversion factor for a CRNA service not meeting the medically directed requirements “may not exceed the allowance for a service personally performed by a physician.”

One reporting consequence follows from the split: the physician who medically directs a qualified nonphysician anesthetist “would ordinarily report the same time as the qualified nonphysician anesthetist reports for the service.” Divergent times on the paired claim lines are a visible inconsistency.

The QZ decision

QZ is the most consequential modifier on this list because it is the only one that asserts a negative. It says no physician medically directed the case. It is restricted to CRNAs — the manual lists QX, QZ and QS as the modifiers used by qualified nonphysician anesthetists, but QZ is defined specifically as “CRNA service: Without medical direction by a physician,” and anesthesiologist assistants, who must practice under physician direction, report QX instead.

QZ is correct in genuinely independent practice. It becomes a compliance problem when it is used as a default — billed on cases where an anesthesiologist was in fact involved, because QZ pays the CRNA at the full rate rather than half, and because it avoids having to prove the seven medical direction steps. The record then contains an anesthesiologist’s signature on a pre-anesthetic evaluation while the claim asserts no physician direction occurred. That internal contradiction is what reviewers look for, and it is visible without any clinical judgement.

The teaching CRNA case

QZ also carries the teaching CRNA scenarios. A teaching CRNA who supervises a single case involving a student nurse anesthetist, and is continuously present, reports QZ; no Part B payment is made for the student’s service. Where a teaching CRNA covers two concurrent student cases, full base units are recognized if the CRNA is present throughout pre- and post-anesthesia care, and time is counted only for periods of personal presence — which, uniquely here, may be discontinuous.

The AA + QZ exception

There is one narrow circumstance in which a physician and a CRNA are both paid in full for the same case. CMS provides that “in unusual circumstances when it is medically necessary for both the CRNA and the anesthesiologist to be completely and fully involved during a procedure, full payment for the services of each provider is allowed.” The physician reports AA and the CRNA reports QZ, and “documentation must be submitted by each provider to support payment of the full fee.”

This is not a workaround for a busy room. It requires that both providers were completely and fully involved, that this was medically necessary, and that both submit supporting documentation. Used routinely, it is indefensible; used correctly, it is the only path to full payment for both.

Worked examples

Example 1 — four rooms, mixed payers

An anesthesiologist oversees four concurrent cases: two Medicare, one commercial, one self-pay. She performs the pre-anesthetic evaluation on all four, prescribes each plan, is present at induction and emergence in each, monitors at frequent intervals, remains in the suite, and provides post-anesthesia care. Result: four concurrent cases, all seven steps met. QK on the physician line, QX on each CRNA line, 50/50 split. The non-Medicare cases still count toward concurrency, and here they land exactly at the limit.

Example 2 — the fifth room

Same physician, same day, a fifth room opens and she takes it on. Result: more than four concurrent procedures. The physician’s service is medical supervision, not medical direction. AD applies, and the MAC may allow only three base units per procedure — plus one additional time unit per case only where she can document presence at induction. Adding the fifth room reduced the physician’s payment across all five.

Example 3 — the recovery room detour

An anesthesiologist directing three concurrent cases steps out to discharge two patients from the recovery room and to handle the afternoon schedule. Result: both activities are on the CMS list of things that do not substantially diminish scope of control. Medical direction is intact; QK stands.

Example 4 — the labor floor

The same physician instead goes to the labor floor and provides continuous monitoring of an obstetric patient for the next hour. Result: CMS permits periodic rather than continuous obstetric monitoring, and permits administering a labor epidural. Continuous monitoring is neither. She has left the immediate area for other than a short duration and is not available for immediate response; the three cases do not meet the requirements for the medically directed rate.

Example 5 — one CRNA, one physician

An anesthesiologist directs a single CRNA on a single case and meets all seven steps. Result: QY from the physician, QX from the CRNA, each paid 50 percent of what the anesthesiologist alone would have been allowed. QK would be wrong here — it is defined for two, three or four concurrent procedures.

Documentation that survives review

CMS tells MACs to look. The manual directs contractors to “perform reviews of payments for anesthesiology services to identify situations in which an excessive number of concurrent anesthesiology services may have been performed,” and to “periodically review a sample of claims for medical direction of four or fewer concurrent anesthesia procedures.” During that process, physicians may be asked to submit documentation of the names of procedures performed and the names of the anesthetists medically directed.

The consequence for failing that request is prospective and expensive: physicians “who cannot supply the necessary documentation for the sample claims must submit documentation with all subsequent claims before payment will be made.”

A record built to survive this contains, at minimum: a signed pre-anesthetic examination and evaluation; the prescribed anesthesia plan; an explicit attestation of presence at induction and emergence; contemporaneous evidence of monitoring at intervals; a post-anesthesia note; identification of the qualified individual performing each delegated element; and, where the group practice split is used, the identity of each physician who furnished each component. If your group is defending concurrency, an accurate room-by-room time grid covering all patients, not only Medicare beneficiaries, is the document that settles the question. For how contractor review escalates once a pattern is identified, see our guide to the RAC audit process, triggers and appeal levels.

Where payers differ

Everything above is Medicare policy under Pub. 100-04. Commercial and workers’ compensation payers frequently adopt the same modifier set and the same seven-step definition by reference, but not always the same payment consequences: medical direction percentages, whether QZ is paid at parity with a physician-performed service, and whether the payer recognizes AD at all are contract terms rather than settled national rules. State scope-of-practice law is a separate layer again — whether a CRNA may practice without physician direction in a given facility is governed by state law and facility policy, not by the modifier.

Frequently asked questions

Can an anesthesiologist assistant report QZ?

No. CMS defines QZ as “CRNA service: Without medical direction by a physician.” Anesthesiologist assistants report QX, the medically directed nonphysician anesthetist modifier. CRNAs are identified on the provider file by specialty code 43 and anesthesiologist assistants by specialty code 32.

Does QS replace the payment modifier for a MAC case?

No. CMS states that QS “can be used by a physician or a qualified nonphysician anesthetist and is for informational purposes,” and that providers “must report actual anesthesia time and one of the payment modifiers on the claim.” The payment modifier goes in the first field; QS goes in the second. Monitored anesthesia care is paid “on the same basis as other anesthesia services.”

Do non-Medicare cases count toward the four-case concurrency limit?

Yes. CMS is explicit that concurrency “is not dependent on each of the cases involving a Medicare patient,” and gives the worked example of three concurrent procedures involving two non-Medicare patients and one Medicare patient counting as three concurrent cases.

What is the difference between medical direction and medical supervision?

Medical direction is two to four concurrent cases with all seven required activities performed and documented, paid at 50 percent of the physician-alone allowance. Medical supervision is what CMS pays when the physician exceeds four concurrent procedures or is performing other services while directing: modifier AD, and only three base units per procedure, with one possible additional time unit where presence at induction is documented.

If the physician only missed the post-anesthesia care step, can we still bill QK?

No. The seven activities are cumulative conditions for payment at the medically directed rate, and providing indicated post-anesthesia care is one of the four elements CMS separately requires to be documented. If a required activity was not performed, the case did not meet the medical direction standard, regardless of how the remaining six were handled.

Can the pre-anesthetic evaluation and post-anesthesia care be done by different physicians?

Yes, within a group practice. One physician member may provide the pre-anesthesia examination and evaluation while another fulfills the other criteria, and one member may provide post-anesthesia care while another furnishes the remaining components — provided the medical record identifies which physician furnished each service.

Related guides

Modifier 47: Anesthesia by the Surgeon, and What It Cannot Do — the separate question of a surgeon administering regional or general anesthesia for their own procedure.
Modifiers 62 and 66: Co-Surgeons and the Surgical Team — the surgical analogue of splitting one service between multiple practitioners.
Modifiers 80, 81, 82 and AS: When an Assistant at Surgery Is Payable — the assistant-at-surgery decision and its documentation requirements.
RAC Audit: Triggers, Review Types, ADR Timelines, and the Five-Level Appeal.

Sources

Centers for Medicare & Medicaid Services, Medicare Claims Processing Manual (Pub. 100-04), Chapter 12, §50 — Payment for Anesthesiology Services (Rev. 3747; effective 01-01-17).
CMS, Medicare Claims Processing Manual (Pub. 100-04), Chapter 12, §140.3 — Anesthesia Fee Schedule Payment for Qualified Nonphysician Anesthetists (Rev. 3883; effective 01-16-18).
CMS, Medicare Claims Processing Manual (Pub. 100-04), Chapter 12, §§140.4–140.5 — Special Billing and Payment Situations; Payment for Anesthesia Services Furnished by a Teaching CRNA (Rev. 3747; effective 01-01-17).