Anesthesia Billing: Base Units, Time Units, and the Modifiers That Matter

by | Mar 6, 2026 | Compliance & Risk

anesthesia billing compliance

Anesthesia billing is built on a unit-based formula that is unlike any other specialty. The 2026 conversion factor is $20.4976. But the modifiers – QK, QY, QZ, and AD – determine whether you collect 50 percent, 100 percent, or three base units. Get them wrong at scale and the exposure is significant.

Key Takeaways

  1. The 2026 CMS anesthesia conversion factor is $20.4976 per unit. Payment is calculated as (base units + time units) multiplied by the conversion factor, with one time unit equal to 15 minutes of continuous anesthesia time.
  2. Modifier AA means the anesthesiologist personally performed the case at 100 percent. QK and QY indicate medically directed services at 50 percent each for physician and CRNA. QZ means the CRNA performed without medical direction at 100 percent. AD – more than four concurrent cases – limits the physician to three base units plus one time unit for documented induction.
  3. The TEFRA seven conditions at 42 CFR 415.110 are the legal predicate for billing QK or QY. Any condition that cannot be documented for a given case turns a legitimate claim into a potential overpayment.
  4. Payer rules on anesthesia modifiers are not uniform. What CMS accepts is not always what Blue Cross or Aetna accept for the same claim. Your billing team needs a payer-specific modifier grid, not a single policy applied to all payers.

Anesthesia billing is structured differently from nearly every other specialty in medicine. Rather than submitting a CPT code with a standard relative value unit calculation, anesthesia claims are built on a unit-based formula: a fixed number of base units assigned to each anesthesia procedure code, plus time units accrued in 15-minute increments throughout the case, multiplied by a conversion factor set by the payer. For 2026, the CMS conversion factor is $20.4976 per unit for standard Medicare participating physicians. A routine general surgery case assigned 7 base units that runs 90 minutes generates 7 + 6 = 13 units, billed at $20.4976 per unit, for a Medicare allowed amount of $266.47 before the physician’s participation discount. That arithmetic is the same across tens of thousands of claims per year for a busy group, which means errors in the formula – or in the modifier that determines what percentage of the fee schedule applies – compound quickly.

The modifiers are where most of the compliance risk lives. They are not optional documentation fields; they are the claim-level assertions about who provided the anesthesia service, under what supervision arrangement, and therefore what the payer owes. An incorrect modifier is not a technicality. It is a representation to the payer about a fact. At audit scale, a modifier pattern that does not match the documentation in the clinical record is the definition of a billing compliance problem, and the False Claims Act implications for groups that bill Medicare or Medicaid are not academic.

The Modifier Map

The core modifiers and their payment consequences under Medicare are:

  • AA – Anesthesia services personally performed by an anesthesiologist. The physician was present and in continuous attendance for the entire procedure. Billed at 100 percent of the fee schedule by the physician. This is the only modifier where the physician captures the full unit value of the case.
  • QK – Medical direction of two to four concurrent CRNA procedures. The anesthesiologist is medically directing multiple simultaneous cases. The physician bills at 50 percent; the CRNA in each directed case bills with modifier QX at 50 percent. The 50/50 split totals 100 percent per case – the same as AA on an aggregate basis, but now divided between two providers and two claims.
  • QY – Medical direction of one CRNA. Same payment structure as QK but for a single directed case. Fifty percent to the physician, 50 percent to the CRNA under QX.
  • QZ – CRNA without medical direction. The CRNA performed the anesthesia service without physician direction. The CRNA bills at 100 percent of the CRNA fee schedule. This modifier is available in states that have opted out of the federal physician supervision requirement. Note that UnitedHealthcare announced a 15 percent payment reduction on QZ claims effective October 2025 in most states – a development that groups with significant QZ volume must factor into their revenue projections.
  • AD – Medical supervision of more than four concurrent procedures. The anesthesiologist is supervising more than the TEFRA maximum. Medicare limits the physician’s payment to three base units per case, plus one time unit if the physician was present and documented at induction. This is a significant payment reduction from the QK structure, and it is the consequence of exceeding the four-case limit that the TEFRA conditions permit.

The Seven TEFRA Conditions

The legal basis for billing QK or QY – rather than being limited to AD – is 42 CFR 415.110, which defines seven conditions the anesthesiologist must meet for each medically directed case. The conditions require the physician to perform the pre-anesthetic examination and evaluation, prescribe the anesthesia plan, personally participate in the most demanding procedures in the anesthesia plan including induction and emergence, ensure that any procedure in the anesthesia plan that they perform themselves is not delegated to another physician, monitor the course of anesthesia at frequent intervals, remain physically present and available for immediate diagnosis and treatment of emergencies, and provide indicated post-anesthesia care.

These are not aspirational standards. They are the predicate for the claim. If a physician directed four rooms during a period when three were inducing simultaneously, personal presence at induction for each case cannot have been met for at least two. Billing QK on all four is a false attestation on three claims. Groups that operate at or near the four-case limit in high-volume settings with clustered case starts should have scheduling and documentation practices reviewed by compliance counsel before the next payer audit identifies the pattern.

The modifier is a representation, not a selection. If the documentation cannot support the conditions the modifier asserts, the exposure belongs to whoever signed the claim.

Where the Documentation Breaks Down

In most groups with a billing compliance problem, the breakdown is not intentional. It is systemic. The billing team applies modifiers based on the provider type in the schedule – physician or CRNA – without reviewing whether the documentation for each case supports the specific conditions for medically directed status. The anesthesiologist signs off on cases at end of day without reviewing whether the time-stamp record shows they were simultaneously present at induction in overlapping rooms. The CRNA notes do not consistently document whether the physician performed the pre-anesthetic examination or delegated it.

Fix this at the process level, not the claim level. The documents your group needs are: a written medical direction policy that maps each of the seven TEFRA conditions to a specific documentation requirement, a concurrent case tracking log that shows physical location of the directing physician at each condition-triggering moment, and a pre-billing review step where the biller confirms the documentation record before applying QK or QY. None of that requires new software. It requires someone to sit with the current documentation flow, identify where the condition evidence is missing or ambiguous, and build the forms or checklists that capture it going forward. That is operational work, not legal work, and it is where the compliance exposure is actually closed.

Commercial Payer Rules Are Not CMS Rules

One of the most common billing errors in anesthesia is treating Medicare modifier rules as universal. They are not. Commercial payers maintain their own billing policies that differ in meaningful ways. Some do not recognize the QK/QX split and require a single claim under the physician’s NPI, treating the CRNA as incident-to. Others accept QZ claims at a different percentage than QK. Some require different documentation to support medical direction than Medicare does.

Your billing team needs a payer-specific modifier grid: for each major payer in your panel, the accepted modifier set, the payment percentage for each modifier, and any documentation requirements that differ from the Medicare standard. This is not a document most billing vendors maintain proactively. It is built by pulling payer policy documents, confirming rules with provider relations, and auditing a sample of recent claims. If your group has not done that audit in the last 18 months, the grid you are operating from is likely out of date.

From the Field

A five-anesthesiologist group in the Mountain West contracted with a new billing vendor two years ago and assumed the vendor was managing modifier compliance. A routine pre-audit self-review found that a significant share of QK claims submitted over the prior year lacked documentation of the pre-anesthetic examination by the directing physician – one of the seven TEFRA conditions. The vendor had been applying QK based on scheduling data showing physician and CRNA together on a case, without any review of whether the clinical documentation supported each condition. Our engagement built a documentation checklist keyed to the seven conditions, sat with the billing coordinator and the lead anesthesiologist to redesign the end-of-case sign-off process, and worked through a targeted re-review of the prior claims to assess refund exposure. The group made a voluntary repayment on the claims that could not be supported, filed a corrective action plan, and put the new process in place. The refund was manageable; the alternative – a government audit following a whistleblower complaint – would not have been.

Consulting or Fractional Engagement for Billing Compliance

A billing compliance audit is a consulting deliverable. The output is a findings report, a corrective action plan, and a set of policy templates. If your group has a billing manager who can implement the corrective policies and maintain them going forward, an outside consultant who produces that deliverable and hands it off may be the right and more economical choice for your situation.

The fractional engagement makes sense when the implementation is the hard part: rebuilding the documentation workflow requires someone to sit in the EMR with the lead anesthesiologist and redesign the end-of-case attestation template, then train every provider who signs claims on the new process, then run the first 90-day audit to confirm compliance is holding. That work does not happen when the corrective action plan sits in an email thread. Be a careful buyer: “fractional compliance officer” is an unregulated label, and some firms use it to describe what is functionally a consulting retainer with periodic check-ins. Ask whether the person will be working in your billing system with your billing coordinator or delivering documents and reviewing them remotely. Both have value; only one closes the documentation gap at the claim level.

Sources

  1. 42 CFR 415.110 – Conditions for payment: Medically directed anesthesia services (TEFRA rules) — https://www.ecfr.gov/current/title-42/chapter-IV/subchapter-B/part-415/subpart-C/section-415.110
  2. CMS, CY 2026 Physician Fee Schedule Final Rule – Anesthesia Conversion Factor ($20.4976) — https://www.cms.gov/medicare/payment/fee-schedules/physician/anesthesiologists-center
  3. Coronis Health, Cracking the Code: Qualifying and Quantifying the QZ Modifier — https://www.coronishealth.com/blog/cracking-the-code-qualifying-and-quantifying-the-qz-modifier
  4. Ventra Health, 2026 CMS Final Rule Anesthesia Revenue Impact — https://ventrahealth.com/blog/2026-cms-final-rule-impacts-on-anesthesia/

More in the Anesthesiology Series

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