How anesthesia billing units work: base, time, modifiers, then the conversion factor
Anesthesia payment is (base units + time units + modifying units) × conversion factor. That formula is why a general medical biller underpays you. ClearBilling is a USA-based, woman-owned firm that has billed this formula for over 25 years.
Base units
Each anesthesia CPT (generally 00100 to 01999) maps to ASA base units for the procedure. Harder cases carry more base. The crosswalk has to be current. Using last year's ASA RVG, or picking a nearby CPT because the record was vague, is silent leakage.
Time units
Medicare typically uses 15-minute time units, with rounding rules that depend on the payer. Time starts when the anesthesiologist or CRNA begins preparing the patient in the OR / procedure room (or per the payer's definition) and ends when the patient can be safely placed under postoperative care. Relief, breaks, and discontinuous time have rules. Appointment slot time is not anesthesia time.
OB and labor epidurals are a special case: some payers want incremental time, some want a flat delivery fee, some want full time. One methodology applied nationally will be wrong.
Modifying units
Physical status P1 to P6 adds units when the payer recognizes them (Medicare generally does not pay extra for P3 to P5 the way many commercials do). Qualifying circumstances (extreme age, hypothermia, hypotension, emergency) add more when documented. Bill them only when the record supports them.
Conversion factor
Medicare publishes a national anesthesia conversion factor (adjusted geographically). Commercial contracts often have their own. If your biller applies Medicare CF to a commercial plan, or never notices a contracted CF change, you are donating points. See the conversion factor page.
FAQ
Straight answers for practices comparing anesthesia billing companies.
Is anesthesia billed like surgery CPT fees?
No. Surgery is usually a fee schedule line. Anesthesia is unit-based. That is the whole point of hiring a specialist.
Who sets base units?
ASA publishes base units. CMS and many payers adopt them. Your biller should be on the current crosswalk.
Do all payers round time the same way?
No. Never assume a 15-minute Medicare rule applies to every commercial contract.
Related
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