CPT 45378 is a diagnostic flexible colonoscopy; CPT 45380 is a colonoscopy with biopsy, single or multiple. Most denials on both codes trace to one error: the claim never tells the payer the procedure began as a screening. Medicare wants G0121 or G0105, or modifier PT once a biopsy happens; many commercial payers want modifier 33.
Colonoscopy denials rarely come from the endoscopy itself. They come from a mismatch between what the scheduler booked, what the physician found, and what the claim says. Get that sequence right and most of these denials, and the angry patient calls that follow them, go away.
The two codes, and why they are almost never billed together
AAPC’s General Surgery Coding Alert (19 July 2022) gives the descriptors: 45378 is “Colonoscopy, flexible; diagnostic, including collection of specimen(s) by brushing or washing, when performed (separate procedure),” and 45380 is “Colonoscopy, flexible; with biopsy, single or multiple.”
Two details in that language drive denials:
- “Separate procedure.” CMS’s NCCI Policy Manual, Chapter VI (revision date 1 January 2026), states that surgical endoscopy includes diagnostic endoscopy and that a diagnostic endoscopy code shall not be reported with a surgical endoscopy code. Billing 45378 and 45380 for the same session will hit that edit.
- “Single or multiple.” Five biopsies are still one unit of 45380. CMS’s practitioner MUE table effective 1 October 2026 allows one unit per date of service for both 45378 and 45380.
The CMS relative value file released 26 August 2026 (RVU26D) lists 45378 as the endoscopic base code for 45380 and gives both a 000 global period. When a biopsy and a snare polypectomy are done on the same day, the same NCCI chapter says the edit pairing 45385 with 45380 may be bypassed with modifier 59 or XS only when the two procedures were performed on separate lesions.
Screening or diagnostic: the order decides
AAPC’s 17 May 2024 guidance is to code based on how the provider ordered the procedure. A patient with rectal bleeding or anemia is having a diagnostic colonoscopy even if the referral says “screening,” and that claim takes no screening modifier. An asymptomatic patient booked for screening stays a screening patient unless the physician actually does something therapeutic or diagnostic, such as a biopsy or polyp removal.
Findings alone do not convert the procedure. AAPC’s July 2022 guidance is explicit: hemorrhoids, diverticulosis or an anal fissure noted during a screening are reported as secondary diagnoses after Z12.11, and the procedure code does not change.
Medicare: G0121, G0105 and modifier PT
Medicare does not use 45378 for a screening. The Medicare Claims Processing Manual, Chapter 18, §60.2 assigns the screening to HCPCS G0121 (colonoscopy on an individual not meeting criteria for high risk) or G0105 (colonoscopy on an individual at high risk), with frequency limits counted in months:
- G0121: once every 10 years, meaning at least 119 months must pass after the month of the last covered screening colonoscopy, or 47 months after a covered screening flexible sigmoidoscopy (G0104).
- G0105: once every 24 months, meaning at least 23 months after the month of the last covered G0105.
Pick the wrong risk code and the claim fails frequency or diagnosis edits even when the patient qualified under the other one.
When a lesion is biopsied or removed, §60.2 instructs that the diagnostic code, such as 45380, be billed with modifier PT instead of G0121 or G0105. CMS’s MLN006559 preventive-services page (July 2026) adds that PT goes on at least one line of the claim to show a screening became diagnostic or therapeutic. Anesthesia follows the same logic under Chapter 18, §60.1.1: 00812 for a screening colonoscopy, 00811 with PT once it converts. Moderate sedation (G0500 or 99153) takes modifier 33 for a screening and PT after conversion. That is the one place Medicare itself uses modifier 33 on a colonoscopy claim.
Two more Medicare rules catch practices out:
- Follow-on colonoscopy after a positive stool test. Since 1 January 2023, a colonoscopy following a positive non-invasive stool-based test is a screening, identified with modifier KX, and the usual frequency limits do not apply (Chapter 18, §60.2).
- Same-day visit. CMS’s Global Surgery booklet (MLN907166, December 2025) includes the endoscopy-day evaluation in the procedure payment unless the provider performs a significant, separately identifiable E/M service, reported with modifier 25.
What changes on 1 January 2027
This one is statute, not a proposal. Section 122 of Division CC of the Consolidated Appropriations Act, 2021 phases out the coinsurance on a screening that becomes diagnostic. Chapter 18, §60.1.1 sets it out: for dates of service in CY 2023 through CY 2026, the deductible is waived and coinsurance is 15 percent when PT is on the claim. For CY 2027 through CY 2029 it drops to 10 percent. From 1 January 2030 it is waived entirely.
Update patient estimates and front-desk scripts for January dates of service. A missing PT modifier does not just cost the lower coinsurance. It prices the whole encounter as a diagnostic colonoscopy with the deductible applied.
Commercial payers: 45378 with modifier 33
Commercial payers that do not recognize the Medicare G-codes expect 45378 with modifier 33 for a screening, according to AAPC (May 2024). State Medicaid programs set their own rules, so check the program’s billing manual. When the screening converts, AAPC’s July 2022 guidance shows 45380 with modifier 33 for non-Medicare payers and PT for Medicare. The May 2024 AAPC piece adds that many commercial payers also accept PT while others insist on 33, so the payer’s own policy is the tiebreaker.
The Affordable Care Act rules behind this come from joint FAQs published by CMS:
- Part XII, Q5 (20 February 2013): polyp removal during a colonoscopy performed as a screening is integral to the screening, and plans may not impose cost-sharing for it. Treatment that is not itself a recommended preventive service can still carry cost-sharing.
- Part 51, Q7 and Q8 (10 January 2022): plans subject to PHS Act section 2713 must cover a colonoscopy after a positive stool-based or direct-visualization screening test without cost-sharing, for plan years beginning on or after 31 May 2022.
When a commercial claim for a converted screening prices as diagnostic, the payer applies the deductible, the patient receives a bill they were told they would not get, and the practice ends up correcting and resubmitting the claim anyway. The modifier is what prevents that.
The colonoscopy pre-bill check
- The order and pre-procedure note say “screening” or “diagnostic,” and symptoms mean diagnostic with no 33 or PT.
- For Medicare, G0121 versus G0105 matches the documented risk history, and the frequency is counted in months after the prior procedure’s month.
- A converted screening is billed with the surgical code, such as 45380 or 45385, plus PT for Medicare or 33 for payers that require it. Never a G-code plus 45380.
- Never 45378 with 45380 for the same session.
- One unit of 45380 no matter how many biopsies. Biopsy plus snare on separate lesions uses 59 or XS.
- Anesthesia and sedation lines carry modifiers that match the procedure line.
- A follow-on colonoscopy after a positive Medicare stool test carries KX.
- Z12.11 is first-listed for a screening, and findings follow it.
Our gastroenterology billing guide covers the rest of the GI code set, and coding quick-references live in the AMS resources library. When screening-to-diagnostic conversions keep coming back denied or mis-priced, that payer-by-payer modifier logic is what our medical billing services team has handled for practices since 1992.
