Key takeaways
- Screening colonoscopies that turn therapeutic are the most common GI billing error: Medicare needs modifier PT and most commercial plans need modifier 33, with the screening diagnosis listed first.
- For Medicare, a screening colonoscopy that becomes diagnostic carries a reduced 15% patient coinsurance through December 31, 2026, phasing down to zero by January 1, 2030.
- GI practices bill across settings (office, ambulatory surgery center and hospital) and often for infusions of biologics, so a GI billing company needs site-of-service and drug billing skills.
- Prior authorization for biologics and some procedures is where many GI denials start.
- Ask every gastroenterology billing company the same 10 questions, test them on the same de-identified claims, and score them side by side.
What makes gastroenterology billing different
- Screening versus diagnostic endoscopy. The same colonoscopy is billed differently depending on why it was done and what was found, with different codes for Medicare (G0105, G0121) and other payers, and modifiers PT or 33 when screening becomes therapeutic. Our colonoscopy billing guide covers the rules.
- Multiple procedures in one session. An upper endoscopy and a colonoscopy on the same day, or several techniques in one scope, follow multiple-endoscopy payment rules and NCCI edits.
- Site of service. The physician's professional claim, the ambulatory surgery center facility claim and the anesthesia claim all have to agree. See our ASC billing services for the facility side.
- Infusions and biologics. Practices that infuse biologics for inflammatory bowel disease bill drug units, JW or JZ, and infusion administration codes, and need authorizations that renew.
- Pathology and patient questions. Patients often expect a "free" screening and then receive bills for pathology, anesthesia or a polypectomy. Clear coding and good statements reduce calls and write-offs.
Signs your GI billing needs a change
- Screening colonoscopy claims denied, or patients billed when they should not be.
- Professional and ASC claims that disagree on codes or modifiers.
- Biologic infusions denied for authorization or units.
- Days in AR rising, or a growing share of AR older than 90 days. Our days in AR guide shows the formula.
10 questions to ask a gastroenterology billing company
- Which GI practices do you bill for today, and in which settings? Office, ASC and hospital-based groups work differently. Ask for a reference that matches yours.
- How do you code a screening colonoscopy that becomes therapeutic? Ask them to walk through Medicare (PT) and a commercial plan (33), including diagnosis order.
- How do you handle follow-on colonoscopies after a positive stool or blood-based screening test? Payers now treat many of these as part of screening (Medicare uses the screening code with modifier KX after a positive stool-based test), which changes patient cost-sharing.
- How do you bill multiple endoscopies on the same day? Look for knowledge of multiple-endoscopy rules and NCCI edits, not just modifier 59 on everything.
- Do you bill the ASC facility claim too, and how do you keep it consistent with the professional claim?
- How do you bill biologic infusions? Ask about drug units, JW and JZ, infusion hierarchy and authorization tracking.
- Which GI systems do you work in? gGastro, Provation, athenahealth, NextGen and others have their own charge workflows. Working inside your system keeps your data with you.
- What does the percentage cover, and what is extra? Get included and excluded services in writing, and confirm the fee applies to net collections.
- What will we see each month? At minimum: collections, AR aging, denial rate by reason, clean claim rate and screening-claim denials.
- Who owns the data, and what happens if we leave? Payer accounts should stay in your practice name, payments should go to your bank account, and open AR should be handed back on a written timeline.
Worked example: a Medicare screening colonoscopy with a polyp removed
A 67-year-old Medicare patient comes in for a routine screening colonoscopy. The gastroenterologist finds a polyp and removes it with a snare.
| Item | Correct billing | Common error |
|---|---|---|
| Procedure code | 45385-PT (colonoscopy with snare removal, screening turned therapeutic) | G0121 (screening only), or 45385 without PT |
| Diagnosis order | Z12.11 (encounter for screening for malignant neoplasm of colon) first, then the polyp finding | Polyp diagnosis only |
| Patient cost | Reduced 15% coinsurance for dates of service in 2026 | Full diagnostic cost-sharing, or a denied claim and a confused patient |
For a commercial plan, the same case is usually billed 45385-33 with the screening diagnosis first. Ask each company how they would bill this exact visit for your top three payers.
How gastroenterology billing companies charge
Most charge a percentage of net collections; some charge per claim or a flat monthly fee. Ask whether ASC facility billing, anesthesia billing and patient statements are included or priced separately, and compare the total cost for the same scope. If you are weighing outsourcing against an in-house team, our in-house vs outsourced billing cost calculator puts both on one page.
Scorecard for comparing two or three companies
Score each company from 1 to 5 on each line, using their written answers and a review of the same 20 de-identified claims.
| What to score | What a 5 looks like |
|---|---|
| GI experience | Current GI clients and a reference in your setting |
| Screening rules | Correct PT, 33 and diagnosis order for each payer |
| Multiple endoscopies | Correct use of multiple-endoscopy rules and NCCI edits |
| ASC and professional claims | One team keeps both consistent |
| Biologic infusions | Units, waste modifiers and authorizations checked before billing |
| Reporting | Monthly KPIs plus claim-level access in your own system |
| Price clarity | One written list of what the rate includes and excludes |
| Exit terms | You own the data and payer accounts, with open AR handed back on a written timeline |
Red flags
- No current GI clients, or no references in your setting.
- Unsure how to bill a screening that becomes therapeutic.
- Modifier 59 used as a default fix for edits.
- A fee based on charges instead of collections.
- Payments deposited into an account you do not control.
- A long contract with no exit plan or data return.
What to check in the contract
- A business associate agreement under HIPAA, and how patient data is accessed.
- Term, minimums and notice needed to end the agreement.
- Who owns the data and payer accounts, and how records come back.
- How open AR is worked after termination.
- Whether ASC, anesthesia and patient statements are included.
- Reporting you receive and how often.
Where PhysiAssist fits
PhysiAssist bills for gastroenterology practices and ASCs. Certified coders check screening-to-therapeutic rules, multiple-endoscopy edits and biologic infusion claims before they go out, and we work inside your systems. PhysiAssist charges 2.8% to 5% of net collections, with no setup fees or minimums; see pricing and our gastroenterology billing services. We would rather you compare us with others using the questions above than take our word for it.
Frequently asked questions
What does a gastroenterology billing company do?
It checks eligibility and authorizations, codes endoscopy, office and infusion claims, submits them, posts payments, works denials and follows up on unpaid claims for a GI practice, and often bills the ASC facility claim too.
How much does a gastroenterology billing company cost?
Most charge a percentage of net collections. PhysiAssist charges 2.8% to 5% of net collections, with no setup fees or minimums. Compare the total cost for the same scope, including ASC billing and patient statements.
What modifier is used when a screening colonoscopy becomes therapeutic?
Medicare uses modifier PT on the colonoscopy code; most commercial plans use modifier 33. In both cases the screening diagnosis is listed first.
Does a Medicare patient pay anything when a polyp is removed during screening?
Yes, a reduced coinsurance. For dates of service through December 31, 2026 it is 15%, and it phases down to zero by January 1, 2030.
Should a GI practice outsource billing for its ASC too?
Often yes, because the facility and professional claims for the same case have to agree. One team billing both reduces mismatches and denials.
Sources
- Becker's ASC Review, What CMS colorectal cancer screening policy change means for ASC reimbursement in 2026 (July 7, 2026: 15% coinsurance through December 31, 2026, phasing to zero by January 1, 2030).
- CMS Medicare Claims Processing Manual, Chapter 18: colorectal cancer screening, codes G0105 and G0121 and modifier PT.
- American Medical Association, CPT 2026: colonoscopy codes 45378 to 45398 and modifier 33.