What Colonoscopy Billing Changes Take Effect in 2027?
Two significant changes affect gastroenterology billing in 2027. First, the Medicare colonoscopy cost-sharing phase-down established by the Consolidated Appropriations Act of 2021 drops patient coinsurance from 15% to 10% when a screening colonoscopy converts to a therapeutic or diagnostic procedure during the same encounter, such as when a polyp is found and removed. Second, the American Cancer Society’s 2026 guideline update added the Shield blood-based biomarker test as an official colorectal cancer screening option, creating a new billing workflow for GI practices that order and manage positive results, including the follow-up screening colonoscopy.
Cost sharing drops January 1, 2027: Patient coinsurance on screening-to-diagnostic colonoscopy conversions falls from 15% to 10% for 2027 through 2029, reaching 0% by 2030. This affects every GI practice that bills Medicare for screening colonoscopies with polyp removal.
Blood-based screening enters the workflow: Shield, the first FDA-approved blood test for CRC screening, is now covered by Medicare at $0 for eligible Part B patients ages 45 to 85. A positive result requires a follow-up screening colonoscopy, which GI practices bill and manage.
Billing system updates needed: Fee schedules, patient cost-share calculations, and front-desk collection workflows must be updated before January 1, 2027, to reflect the new 10% coinsurance rate.
The Colonoscopy Cost-Sharing Phase-Down Explained
When a Medicare beneficiary goes in for a routine screening colonoscopy and the gastroenterologist finds and removes a polyp during the procedure, the billing code changes from CPT 45378 (screening colonoscopy) to CPT 45385 (colonoscopy with polypectomy) or CPT 45380 (colonoscopy with biopsy). Medicare classifies the therapeutic codes as diagnostic rather than preventive, which triggers patient cost-sharing.
Before 2023, the patient would owe the full Part B deductible plus 20% coinsurance on the diagnostic portion. Section 122 of the Consolidated Appropriations Act of 2021 created a phase-down schedule that reduces this cost-sharing over time. The Part B deductible is waived for the converted procedure. The coinsurance follows this schedule:
| Year | Patient Coinsurance | Deductible |
| 2023 through 2026 | 15% | Waived |
| 2027 through 2029 | 10% | Waived |
| 2030 and beyond | 0% | Waived |
For GI practices, the practical impact of the January 2027 change is that patient financial responsibility decreases on every screening colonoscopy that converts to a therapeutic procedure. This sounds like a benefit for patients, and it is, but it also changes the billing workflow. Fee schedules, patient cost estimates, pre-procedure financial counseling scripts, and front-desk collection processes all need to reflect the 10% rate starting January 1, 2027.
The modifier PT (colorectal cancer screening test converted to diagnostic test or other procedure) must be appended to the appropriate CPT code on the claim. This modifier triggers the reduced cost-sharing rules. If your billing team omits modifier PT, the patient may be billed the standard 20% coinsurance and the Part B deductible, which is $283 in 2026. Correcting these billing errors after the fact creates patient complaints, refund processing, and administrative rework.
How Does the Shield Blood Test Change GI Practice Billing?
In May 2026, the American Cancer Society updated its colorectal cancer screening guidelines to include the Shield blood test (made by Guardant Health) as an official screening option. Shield is the first FDA-approved blood-based biomarker test for CRC screening in adults ages 45 and older at average risk. Medicare covers the test at $0 for eligible Part B patients.
When a Shield test returns a positive result, the patient needs a follow-up colonoscopy within six months. Under Medicare rules, this follow-up colonoscopy is classified as a screening colonoscopy, not a diagnostic colonoscopy. This means the follow-up is covered with no patient cost-sharing, as long as no polyps are found. If polyps are found and removed during the follow-up, the screening-to-diagnostic conversion rules apply, and the patient owes the applicable coinsurance (10% starting in 2027).
For GI practices, this creates a new patient pathway. Primary care physicians or other ordering providers prescribe the Shield test. If the result is positive, the patient is referred to a gastroenterologist for a follow-up screening colonoscopy. The GI practice needs to verify the test result, confirm the colonoscopy qualifies as a follow-up screening, apply the correct billing codes (G0105 or G0121 for the screening colonoscopy, or the appropriate therapeutic CPT code with modifier PT if polyps are found), and counsel the patient on what their financial responsibility will be.
The ACS guideline explicitly states that Shield is a non-preferred screening option, meaning it is less effective at detecting precancerous polyps than colonoscopy or stool-based tests. However, for patients who decline all other screening methods, the blood test counts. GI practices should expect a growing volume of positive Shield results converting into colonoscopy referrals as adoption increases.
How to Update Your GI Billing Workflow for 2027
The January 2027 transition requires specific billing workflow changes. Here is the checklist for gastroenterology practices.
1. Update your fee schedule and patient cost-share calculator. Change the coinsurance rate for screening-to-diagnostic colonoscopy conversions from 15% to 10% in your practice management system. Verify that the Part B deductible waiver is correctly applied when modifier PT is used.
2. Train front-desk staff on the new cost-share amounts. Patients will ask what they owe. The answer changes January 1: for screening colonoscopies that convert to therapeutic during the procedure, the patient owes 10% coinsurance with no deductible, down from 15%. Pre-procedure cost estimates must be updated.
3. Verify modifier PT is applied on every qualifying claim. Modifier PT must be appended to the appropriate CPT code when a screening colonoscopy converts to a diagnostic or therapeutic procedure. Without it, the claim processes under standard cost-sharing rules and the patient is overbilled.
4. Build a workflow for Shield blood test follow-ups. Confirm the positive test result, verify the patient’s screening eligibility, schedule the follow-up colonoscopy as a screening procedure, and apply the correct billing codes. If the follow-up discovers polyps, apply modifier PT and bill the 10% coinsurance rate (starting 2027).
5. Review your payer contracts. Medicare Advantage plans are required to cover at least what Original Medicare covers, but cost-sharing structures and prior authorization requirements can vary. Verify with each MA plan how they handle the coinsurance phase-down and the Shield follow-up colonoscopy classification.
6. Audit your 2026 claims for modifier PT compliance. Pull a sample of your screening-to-diagnostic conversion claims from the current year. If modifier PT is missing on any of them, patients may have been overcharged and your practice may need to issue refunds and rebill. It is better to catch this now than in a payer audit.
The colonoscopy cost-sharing phase-down, the new blood-based screening pathway, and modifier PT compliance create billing complexity that many in-house teams are not staffed to manage. If your GI practice needs a billing partner that understands gastroenterology coding at the procedure level, we can match you with one in as little as 30 minutes.
Common Colonoscopy Billing Errors That Cost GI Practices Revenue
Across the billing companies in our network, these are the colonoscopy billing errors that recur most often and cost GI practices the most money.
Missing modifier PT. When a screening colonoscopy converts to a therapeutic procedure and modifier PT is not applied, the patient is billed standard 20% coinsurance plus the Part B deductible instead of the reduced rate. This generates patient complaints, refund requests, and claim corrections.
Billing the wrong screening interval. Medicare covers screening colonoscopy every 120 months for average-risk patients and every 24 months for high-risk patients. Billing a screening colonoscopy before the interval has elapsed results in a denial. Your billing system must track each patient’s screening history and next-eligible date.
Confusing screening vs. diagnostic coding. A colonoscopy ordered because of symptoms (abdominal pain, blood in stool, abnormal lab result) is diagnostic from the start and is coded differently from a routine screening colonoscopy. Diagnostic colonoscopies carry standard Part B cost-sharing (deductible plus 20% coinsurance) with no phase-down. Miscoding a diagnostic colonoscopy as screening, or vice versa, creates billing errors in both directions.
Not documenting the clinical indication in the operative report. Every colonoscopy claim must be supported by an operative report that establishes the clinical basis for the procedure. LCD (Local Coverage Determination) criteria for colonoscopy have tightened, and MAC analytics now flag documentation gaps more aggressively than in prior years. A billing company that understands GI-specific documentation requirements catches these gaps before the claim goes out.
Frequently Asked Questions
What is the patient cost for a screening colonoscopy that finds polyps in 2027?
Starting January 1, 2027, when a screening colonoscopy converts to a therapeutic procedure because polyps are found and removed, the Medicare patient owes 10% coinsurance with no Part B deductible. This is reduced from the current 15% rate that applies through December 31, 2026. By 2030, the coinsurance will be 0%.
Is the Shield blood test covered by Medicare?
Yes. Medicare Part B covers the Shield blood-based biomarker CRC screening test at $0 for eligible patients ages 45 to 85 who are at average risk and show no symptoms of colorectal disease. If the result is positive, Medicare also covers a follow-up screening colonoscopy at $0 as long as no polyps are found during the follow-up.
What is modifier PT and when should it be used?
Modifier PT indicates that a colorectal cancer screening test converted to a diagnostic or therapeutic procedure during the same encounter. It must be appended to the appropriate CPT code (45380, 45384, 45385, or 45388) when a screening colonoscopy discovers polyps or other findings that require intervention. This modifier triggers the reduced coinsurance and deductible waiver under the CAA 2021 phase-down.
How often does Medicare cover screening colonoscopy?
Medicare covers screening colonoscopy every 120 months (10 years) for average-risk patients and every 24 months (2 years) for high-risk patients. A screening colonoscopy is also covered 48 months after a flexible sigmoidoscopy. Your billing system must track each patient’s next-eligible screening date to prevent interval denials.
Will the cost-sharing phase-down affect commercial insurance?
Under the ACA, private insurers are required to cover preventive CRC screening with no cost-sharing, including when a screening colonoscopy converts to a therapeutic procedure. The Medicare cost-sharing phase-down specifically addresses the gap in Medicare coverage that existed before the CAA 2021. Commercial insurance practices should not see a change, but Medicare Advantage plans may have varying cost-sharing structures that need to be verified.
Can a billing company help manage these changes?
Yes. A specialized gastroenterology billing company manages modifier PT compliance, screening interval tracking, LCD documentation requirements, and the fee schedule updates required by the 2027 coinsurance change. Gastroenterology Billing, powered by Billing Service Quotes, connects GI practices with billing partners across all 50 states that have direct experience with colonoscopy billing, screening-to-diagnostic conversion coding, and the specific payer rules that apply to GI procedures.
Next Steps
Update your practice management system to reflect the 10% coinsurance rate for screening-to-diagnostic colonoscopy conversions effective January 1, 2027.
Audit your 2026 claims for modifier PT compliance and address any patient overcharges before year-end.
If your billing team is not already preparing for the coinsurance change and the Shield blood test follow-up workflow, get matched with a specialized GI billing partner. Matching through Gastroenterology Billing is free and typically takes 30 minutes.
Colonoscopy billing is getting more complex in 2027, not less. The cost-sharing phase-down, blood-based screening follow-ups, and tighter LCD documentation requirements all need to be handled correctly on every claim. Gastroenterology Billing, powered by Billing Service Quotes, connects GI practices with vetted billing companies that specialize in gastroenterology coding, modifier compliance, and the procedure-level billing accuracy that determines whether your practice gets paid correctly. More than 2,000 providers have been matched across all 50 states, with billing rates starting at 2.95%. Getting matched is free.
