How is anesthesia for a screening colonoscopy billed (00812 vs 00813)?

What is the difference between 00811, 00812 and 00813?

The code is decided by where the scope went and why, not by how sick the patient was. CMS created the family for CY2018: 00811 is lower intestinal endoscopic procedures, endoscope introduced distal to duodenum, not otherwise specified; 00812 is the same anatomy for a screening colonoscopy; 00813 is combined upper and lower gastrointestinal endoscopic procedures, endoscope introduced both proximal to and distal to the duodenum. The catch-all 00810 was deleted at the same time.

So this is not a severity ladder. 00812 turns on intent, whether the colonoscopy was ordered as a screening, and 00813 turns on scope, whether the session included both an upper and a lower endoscopy. A screening colonoscopy done alongside an EGD under one anesthetic is 00813, and the screening word leaves the code even though nothing about the colonoscopy changed.

The base units, and why the screening code is worth less

CMS finalised 4.00 base units for 00811, 3.00 for 00812 and 5.00 for 00813, and those values still stand. The 00812 figure is the odd one: CMS proposed 4.00, then accepted a revised RUC recommendation of 3.00, built on survey data in which most respondents chose 00910 as the reference code.

Read that against the conversion rule below and it produces a result most groups have never modelled: a screening colonoscopy that stays a screening pays one base unit less than the same case after it converts to a polypectomy. Not more. Getting this family right is ordinary coding work against the current code set, but the money runs opposite to where people look.

Does modifier 33 belong on the anesthesia claim for a screening colonoscopy?

Under current CMS instruction, no. The Medicare Claims Processing Manual, Chapter 18, Section 60.1.1 is the operative text and it is one sentence: anesthesia services furnished in conjunction with and in support of a screening colonoscopy are reported with CPT code 00812 and coinsurance and deductible are waived. No modifier is named. The code carries the preventive status by itself.

The opposite instruction is everywhere, and it has a real history. CMS Transmittal 3232, issued in 2015, did tell anesthesia professionals to append modifier 33 to claims qualifying for the waiver, and named the code to carry it: HCPCS 00810. That code was deleted on 1 January 2018 and replaced by a screening-specific code needing no modifier to say screening. The transmittal was never rewritten for 00812, so the old rule outlived the code it applied to.

Modifier 33 has not disappeared from colorectal screening. It moved. The same manual section requires it on moderate sedation, reported with G0500 or 99153, for the waiver to apply there. One rule from the 2015 transmittal still holds and is worth keeping on a laminated card: modifier 33 and modifier PT are never submitted on the same claim line.

The caveat is that contractors and commercial plans run their own edits, and some still expect 33 on 00812, or want 00812 with PT rather than a switch to 00811. That is a payer practice, not current CMS instruction, and the difference decides whether a denial is worth appealing. Confirming each plan in writing belongs in front-end verification, before the schedule fills.

What happens to the anesthesia code when a screening colonoscopy becomes diagnostic?

The anesthesia code changes and picks up a modifier. Chapter 18 Section 60.1.1 again: when a screening colonoscopy becomes a diagnostic colonoscopy, anesthesia services are reported with CPT code 00811 and with the PT modifier, and the deductible is waived. Modifier PT means colorectal cancer screening test converted to diagnostic test or other procedure.

Six steps:

1. Confirm from the order what the colonoscopy was booked as. Screening intent at the time of the order is what makes 00812 available, whatever the scope found.
2. Check what the endoscopist billed. A conversion moves them from G0105 or G0121 to a diagnostic or therapeutic code, and your claim has to agree.
3. If it converted, change 00812 to 00811, rather than leaving 00812 and adding PT, unless that payer has said in writing it wants 00812-PT.
4. Append PT to the 00811 line, and never modifier 33 alongside it.
5. Sequence the screening diagnosis first, then the finding.
6. Record actual anesthesia time in minutes, not units and not a range.

Step two fails silently. In 4 of 5 practices reviewed, nobody reconciled the anesthesia claim against the endoscopist claim, so two halves of one encounter go out disagreeing and only one denies. That is why anesthesia claims for GI endoscopy were denied 2.4 times as often as the procedure claims in our audit: the anesthesia side is billed from the schedule, not the note.

What does Medicare pay for 00812, and why is it less than 00811?

Medicare pays anesthesia on its own formula, not on relative value units: base units plus time units, multiplied by a locality-specific anesthesia conversion factor. One time unit is 15 minutes, and fractions of a 15-minute period are recognised as fractions of a unit.

That last point is where a widely repeated rule is wrong. Medicare does not round time upward into whole units. Chapter 12 Section 50.G tells contractors to divide reported time by 15 and round to one decimal place, and CMS works the example: 88 minutes is 5.9 units, not 6. A 31-minute case is 2.1 time units.

The CY2026 national anesthesia conversion factor is $20.4976 for non-qualifying APM claims and $20.5998 for qualifying APM claims, up from a single $20.3178 in CY2025, both carrying a one-year 2.50% statutory increase.

At 30 minutes of anesthesia time, 00813 allows about $143, 00811 about $123 and 00812 about $102, at CY2026 national rates rounded to the dollar. These carry no geographic adjustment, so check your own locality file before building a fee schedule on them.

A worked example: 1,200 Medicare screening colonoscopy anesthetics a year

Take an anesthesia group covering one endoscopy centre: 1,200 Medicare screening colonoscopy anesthetics a year, averaging 32 minutes each. Assume 40% convert, which is a modelled assumption rather than a measured rate.

32 minutes is 2.1 time units. A case that stays a screening is 3 base units plus 2.1, or 5.1 units, allowing $104.54 at $20.4976. A case that converts is 4 plus 2.1, or 6.1 units, allowing $125.04. The gap is $20.50, exactly one base unit, and across 480 converted cases that is $9,840 a year. It runs the way nobody expects: leaving 00812 on a converted case underpays the group, while the coder who never touches the code thinks they are being conservative.

The same arithmetic prices the time error. Anesthesia time was miscalculated on 8% of cases in our audit, underbilling a median $61 per case. On 1,200 cases that is 96 anesthetics and about $5,856, from minutes delivered, documented and then rounded away.

Do you bill 00813 for a same-session EGD and colonoscopy, and does the screening waiver survive?

Yes to the first, and the second is the question almost nobody answers. When an upper and a lower endoscopy are performed under one anesthetic, 00813 is the code for the session, and you do not report an upper GI anesthesia code alongside 00811 or 00812. It is the general Medicare rule for multiple anesthesia services in one session: pay the highest base unit value, with time encompassing the combined procedures.

The consequence is that the word screening leaves the anesthesia claim. 00813 has no screening variant, and Section 60.1.1 ties the waiver to 00812. A patient who arrives for a screening colonoscopy and has reflux worked up in the same anesthetic has an anesthesia claim that no longer looks preventive, while the colonoscopy is still a screening on the endoscopist claim.

Two things follow for whoever schedules these. Combining an EGD with a screening colonoscopy is a financial decision for the patient, not just a clinical convenience. And the two claims look like different encounters to a payer unless someone reconciles them, the same discipline that decides how a multi-procedure endoscopy session is ranked and discounted. Ranking errors underpaid 9% of multi-procedure sessions in our audit.

What does the patient owe when a screening colonoscopy becomes a polypectomy?

Less than most practices tell them, and less every few years. For a colonoscopy that stays a screening, the Part B deductible and coinsurance are both waived, and the waiver reaches the anesthesia explicitly: the regulation defines colorectal cancer screening tests to include screening colonoscopies, including anesthesia furnished in conjunction with the service.

For a screening that converts, Section 122 of Division CC of the Consolidated Appropriations Act of 2021 phased the coinsurance down rather than leaving it at 20%. CMS instructs contractors that where the PT modifier is appended to at least one code on the claim, they waive the deductible and apply a reduced coinsurance of 15% for dates of service in CY2023 through CY2026, 10% for CY2027 through CY2029, and no coinsurance at all from 1 January 2030.

On a 32-minute converted anesthetic allowing $125.04, the patient share is about $25 under the pre-2022 rule, $18.80 in CY2026, $12.50 from CY2027 and nothing from 2030. Before 2022 the beneficiary was liable for the full applicable coinsurance.

One precision point worth not glossing. The phase-down instruction is written around codes billed on the same claim, and the anesthesia claim is separate from the endoscopist claim. The reading that holds is that PT on your own 00811 line puts your claim inside the rule, since the regulation counts anesthesia within the screening benefit. CMS has not written that sentence about anesthesia specifically, so a group with volume here should get its contractor position in writing. Quoting 20% when the rule says 15% produces the avoidable call: in primary care, 1 in 9 patient balance calls was about a preventive visit billed with a cost share.

How do anesthesia time and the provider modifiers change what you get paid?

Three mechanics decide the rest of the claim, none of them about the code.

When the clock starts and stops

Anesthesia time is the period during which an anesthesia practitioner is present with the patient. It starts when the practitioner begins preparing the patient in the operating room or an equivalent area, and ends when the patient may be safely placed under postoperative care. Blocks either side of an interruption can be added together as long as continuous anesthesia care is furnished within those periods, which is the rule that matters in a suite running two rooms.

Which provider modifier, and what it costs

AA, personally performed by the anesthesiologist, pays the full allowance, and so does QZ, a CRNA service without medical direction. QK for medical direction of two to four concurrent procedures and QY for direction of one nonphysician anesthetist each pay 50%, with the anesthetist reporting QX for the other half. Beyond four concurrent cases it becomes medical supervision under AD, allowing only three base units, plus one time unit if presence at induction is documented. Medical direction modifiers did not match between anesthesiologist and CRNA claims on 5% of cases in our audit, the fastest way to leave half an anesthetic unpaid.

What Medicare will not pay for

Two things a commercial contract may reward and Medicare never will. Modifier units are not allowed, meaning additional units for patient health status, risk, age or unusual circumstances. That rules out ASA physical status units for P3 and above, and qualifying circumstances codes 99100 and 99140, which carry a bundled status with no relative values. QS, monitored anesthesia care, is informational only: it never substitutes for a payment modifier, and actual time plus one of AA, QK, QY, QX or QZ still has to be on the claim. Where MAC needs justifying, G8 covers deep, complex, complicated or markedly invasive procedures and G9 a patient with a history of severe cardiopulmonary condition.

What goes wrong most often, and should GI anesthesia billing sit in house?

The failure modes cluster at the front of the process, not at the claim.

Across the GI and anesthesia claims we audit, converted screenings with no PT or 33 modifier account for 14%, endoscopy ranking errors 9%, miscalculated anesthesia time 8%, ASC facility and professional claims disagreeing 6%, and clashing medical direction modifiers 5%.

The denials are worth filing. Appeals filed by Luxen were overturned 68% of the time, and the appeal is short because the record is arithmetic, not narrative: the order, the note, the minutes, the endoscopist claim. The problem is volume, not merit, since 19% of denied claims were never reworked or appealed. That is a queue, which is what denial and AR work handles, and the ASC side needs the same reconciliation as the facility fee and the professional fee on one case.

In house wins whenever one named person owns this rule set and reads remits against it. The whole of it fits on two pages: three codes, three base unit values, one conversion factor, one modifier decision, one time rule. One job, not a department.

The case for a partner is never one code family. Fully loaded in-house billing cost 7.9% of collections for practices under $2M, across 96 practices that shared payroll data, against an outsourced range of 3% to 6%. Across our client practices, first-pass denial rate fell from 14.2% to 6.1% within 90 days and median days in AR dropped from 54 to 33 within 120 days. If you are comparing options, the questions that separate vendors sit on our medical billing companies page, and the whole-cycle view matters more than any one family, which is what revenue cycle management covers. Either way, pull your last 90 days of 00812 claims and count how many should have been 00811 with PT. A billing review runs that against your own remits.

00811, 00812 or 00813: which code carries the case?

The three codes differ on anatomy, on intent and on what the patient ends up owing. This is what changes between them.

One line to hold on to: intent selects between 00811 and 00812, and scope selects 00813 over both of them.

Gastroenterology

The endoscopist claim sets the terms for the anesthesia claim, and a GI practice is the only party that can see both. When a screening converts, the practice moves from G0105 or G0121 to a diagnostic or therapeutic code and appends PT, and the anesthesia group has to follow within the hour or the two claims disagree. The frequency rules also sit here: G0105 for a high-risk patient after 23 months, G0121 for everyone else after 119 months, or 47 months after a screening flexible sigmoidoscopy. A gastroenterology billing process that cannot report monthly conversions is not managing this family at all.

Anesthesia groups and CRNAs

This specialty carries the exposure, because every error above lands on its claim rather than on the endoscopist claim. Two numbers are worth reporting monthly: how many 00812 claims went out in a month, and how many of those sessions produced a therapeutic code on the other claim. A gap between them is converted cases billed at 3 base units instead of 4. The second monthly number is the share of cases where the anesthesiologist and the nonphysician anesthetist modifiers agree, since anesthesia billing loses half an allowance whenever they do not.

Ambulatory surgery centres

Most screening colonoscopies happen here, and the centre produces a third claim that has to agree with the other two. Facility and professional claims disagreed on codes in 6% of ASC cases in our audit, which on a converted screening means the facility claim can show a therapeutic procedure while the anesthesia claim still shows 00812. Deductible and coinsurance handling for the screening benefit has to match across all three, so ASC billing is where the patient statement is either right or indefensible.

Primary care and internal medicine

Primary care orders most of these colonoscopies and bills none of the anesthesia, and everything it controls sits in the order. The referral has to say screening where it is a screening, because that word is what makes 00812 available downstream and what the whole cost-share waiver hangs on. Worth knowing for the conversation with the patient: Medicare sets no minimum age for a screening colonoscopy, and since 1 January 2025 a follow-on screening colonoscopy after a positive stool-based or blood-based biomarker test is itself a screening test, outside the usual frequency limits.

Hospital outpatient departments

Payment runs on the outpatient prospective payment system rather than the physician fee schedule, so the facility side of the encounter answers to different rules while the anesthesia professional claim still follows everything above. The practical risk in a hospital outpatient setting is organisational rather than technical: the endoscopy suite, the anesthesia group and the hospital billing office are three separate teams, and no one of them owns the reconciliation between the claims they each send.