Anesthesia billing has its own vocabulary, and most CRNAs never get a formal introduction to it. This glossary defines the terms that actually show up in group meetings, pay discussions, and billing reports.
Each entry is short on purpose. For how the terms connect to your income, see /how-crnas-get-paid/ and /anesthesia-collection-rate/.
Key points
- Payment is roughly (base units + time units) x conversion factor.
- Modifiers (QZ, QX, QY, QK, AA) tell payers who did the case.
- Net collection rate, not gross, measures billing performance.
- Missed timely filing deadlines usually mean the money is gone.
Payment building blocks
Base units. A fixed value assigned to each anesthesia CPT code reflecting the complexity of the procedure. A knee scope carries fewer base units than a heart case. Medicare publishes its base unit file annually, drawing on the ASA relative value system.
Time units. Credit for the duration of the anesthetic, from start of continuous care to transfer of care. Medicare counts one unit per 15 minutes; commercial payers may use different increments or rounding rules.
Conversion factor. The dollar amount paid per unit. Payment is roughly (base units + time units) x conversion factor. Medicare's national anesthesia conversion factor is about $20.50 in 2026 and varies slightly by locality. Commercial contracts negotiate their own, usually higher, per-unit rate.
Modifiers. Two-character codes attached to the claim that tell the payer who provided the anesthetic and how. QZ is a CRNA without medical direction. QX is a CRNA with medical direction. QY and QK are the physician side of directed cases, AA is a physician working alone. Wrong modifiers are a top denial cause; see /anesthesia-claim-denials/.
Concurrency. How many cases a provider is involved in at the same time. It determines which modifiers apply and how payment splits in medical direction models. Under Medicare rules, a medically directed case splits the allowed amount between the physician and the CRNA.
Claims and payments
Clean claim. A claim submitted with everything the payer needs to process it on the first pass: correct patient data, codes, modifiers, and times. Clean claim rate measures how often billing gets it right the first time.
Denial. A payer's refusal to pay a claim or claim line, communicated with standardized reason codes. Denials can be corrected, appealed, or written off.
EOB / ERA. Explanation of Benefits and Electronic Remittance Advice. The paper and electronic documents a payer sends explaining what it paid, what it adjusted, and why. The ERA carries the adjustment reason codes billing teams work from.
Assignment. Accepting assignment means the provider agrees to take the payer's allowed amount as payment in full, billing the patient only for their cost-sharing. Medicare participation involves accepting assignment on Medicare claims.
Allowed amount. The contracted price for a service under a specific payer agreement. The gap between billed charges and the allowed amount is the contractual adjustment, which is written off and is not collectible.
Practice finance
Accounts receivable (AR). Money billed and not yet collected. AR is the pile of outstanding claims and patient balances the practice is waiting on.
Days in AR. Average AR divided by average daily charges. It estimates how many days of billing sit uncollected. Rising days in AR means money is arriving slower, often a denial or filing problem.
Gross collection rate. Collections divided by billed charges. Mostly a reflection of how high charges are set.
Net collection rate. Collections divided by allowed amounts. The real measure of billing performance. Full explanation at /anesthesia-collection-rate/.
Credentialing. The process of verifying a provider's qualifications with a facility, and enrolling the provider with each payer so claims can be paid. Payer enrollment lag is a classic cash flow trap for new groups; see /how-to-start-a-crna-group/.
Timely filing. Each payer's deadline for submitting a claim. Medicare generally allows one calendar year from the date of service; commercial deadlines vary by contract. Late claims are denied and usually cannot be billed to the patient.
Stipend / subsidy. A payment from a facility to an anesthesia group covering the gap between collections and the cost of required coverage. Central to hospital contracts; see /crna-group-hospital-contract/.
Why do base units plus time matter to my paycheck?
If you are W2, they mostly do not, day to day. If you are 1099 billing your own cases, or an owner, units are literally your revenue; model it with the /crna-group-revenue-calculator/.
Where can I see official definitions?
Medicare's anesthesia payment rules live in the Claims Processing Manual, Chapter 12. Your commercial contracts define their own terms, and the contract language controls.
This page is general information, not billing or legal advice.
Sources
- CMS Medicare Claims Processing Manual, Chapter 12 (anesthesia rules, modifiers, time units)
- CMS, Anesthesia base units and Physician Fee Schedule files
- Ventra Health, 2026 CMS Final Rule: Impacts on Anesthesia (2026 anesthesia conversion factor)
- X12 Claim Adjustment Reason Codes
- CMS, Medicare timely filing