AMS Solutions provides gastroenterology billing services for GI practices, endoscopy centers and hospital-based GI groups nationwide: coding by AAPC-certified coders, claim submission, denial management, A/R follow-up, prior authorization support and provider credentialing, for a transparent percentage of collections. Physician-founded in 1992; headquartered in Dallas.
Gastroenterology billing is mostly endoscopy billing, and an endoscopy claim has to answer three questions: did the procedure start as a screening, which code in the family describes what was done, and who is billing which piece of the encounter.
Screening vs. diagnostic colonoscopy: modifiers 33 and PT
A colonoscopy booked as a screening stays a screening on the claim unless the physician does something diagnostic or therapeutic, such as a biopsy or polypectomy. Then the claim has to say so, and how differs by payer.
For Medicare, the screening is reported with HCPCS G0121 (not high risk) or G0105 (high risk), per the Medicare Claims Processing Manual, Chapter 18, §60.2. When the screening converts, the surgical code, such as 45380 for a biopsy or 45385 for a snare polypectomy, is billed with modifier PT. CMS’s MLN Matters article MM12656 (revised 30 December 2022) sets out what PT does to the patient’s bill: under Section 122 of Division CC of the Consolidated Appropriations Act, 2021, coinsurance on a screening that becomes diagnostic is 15 percent for dates of service in 2023 through 2026, 10 percent for 2027 through 2029, and nothing from 2030. The anesthesia and sedation codes that carry PT on conversion, 00811, G0500 and 99153, are in the same article.
Commercial payers that do not recognize the Medicare G-codes expect 45378 with modifier 33 for the screening, according to AAPC’s General Surgery Coding Alert (17 May 2024), which adds that some accept PT after conversion while others insist on 33, so each payer’s own policy decides.
A converted screening billed without PT or 33 prices as diagnostic, takes the deductible, and sends the patient a bill they were told they would not get. The code-level walkthrough, including G0121 and G0105 frequency counting, is in our post on CPT 45378 vs. 45380 and why colonoscopy claims deny.
EGD and the multiple-endoscopy rule
AAPC’s General Surgery Coding Alert (18 September 2024) gives the two codes GI practices bill most: 43235, “Esophagogastroduodenoscopy, flexible, transoral; diagnostic, including collection of specimen(s) by brushing or washing, when performed (separate procedure),” and 43239, “Esophagogastroduodenoscopy, flexible, transoral; with biopsy, single or multiple.”
- “Separate procedure.” CMS’s NCCI Policy Manual, Chapter VI (revision date 1 January 2026), states that surgical endoscopy includes diagnostic endoscopy, so 43235 is not reported with 43239 for the same session. AAPC says the same: avoid reporting two codes from the same family together.
- “Single or multiple.” Several biopsies from several sites are one unit of 43239.
- The endoscopic base code. CMS’s Physician Fee Schedule status indicators (Medicare Claims Processing Manual, Chapter 23; page updated 14 July 2026) give endoscopies that share a base procedure a multiple procedure indicator of 3: Medicare applies the multiple-endoscopy rules to the family first, and a base procedure reported with another endoscopy in its family is not paid separately.
Where the NCCI edit allows a modifier, AAPC notes it may be bypassed with modifier 59 under unusual circumstances, such as two instruments for two indications, and only with supporting documentation; our coders read the operative note before any modifier goes on. The worked claim example is in our post on CPT 43239 vs. 43235 and the multiple-endoscopy rule.
Anesthesia, the facility fee and the professional fee
One endoscopy session can produce three claims: professional, anesthesia, and the facility claim from the ambulatory surgery center or hospital outpatient department. The Medicare Claims Processing Manual, Chapter 14 (Rev. 13836, issued 24 June 2026), sets the frame: an ASC bills its facility services on the X12 837 professional format and is paid the ASC amount (§10.1), while the physician and the anesthesiologist bill and are paid for their professional services separately (§10 and §10.4).
The facility and professional claims report the same procedure; the anesthesia claim uses its own code, which for a converted Medicare screening is 00811 with PT (Chapter 18, §60.1.1). The screening and conversion modifiers have to tell the same story on all three. AMS bills the professional side and, where the client contracts for it, the anesthesia and ASC claims; when another party bills one of them, we reconcile before submission. Our guides to ASC facility and professional fees and anesthesia billing cover each side.
Prior authorization and common GI denial patterns
Before a case is scheduled, we check whether the patient’s plan requires prior authorization and obtain it where it does. For Medicare Advantage plans and the Medicaid and CHIP programs and managed care plans covered by CMS’s Interoperability and Prior Authorization final rule (CMS-0057-F, fact sheet 17 January 2024), decisions on standard requests are due within seven calendar days and on expedited requests within 72 hours, and from 2026 the payer must give a specific reason for any denial. Our post on CMS prior authorization rules in 2026 covers the compliance dates.
The common GI denial patterns:
- Screening converted without PT or 33, so the claim prices as diagnostic.
- A Medicare G-code billed with a surgical colonoscopy code for the same session.
- The diagnostic base code billed with the surgical code (45378 with 45380, or 43235 with 43239).
- Modifier 59 or XS on a second endoscopy without documentation of a distinct service.
- Wrong Medicare risk code, G0121 versus G0105, so the claim fails frequency edits.
- Anesthesia or facility modifiers that do not match the professional claim.
- A same-day E/M without a significant, separately identifiable service documented and reported with modifier 25, per CMS’s Global Surgery booklet (MLN907166, December 2025).
Billing and credentialing under one roof
A GI group’s riskiest hand-off is between whoever enrolls a new physician and whoever submits that physician’s first endoscopy claims. At AMS the enrollment dates sit with the team that bills. We file and track Medicare (PECOS), Medicaid and commercial applications, keep CAQH profiles current, and hold a new physician’s claims until enrollment is confirmed. Scope and timelines are on our medical credentialing services page.
Pricing: a transparent percentage of collections
AMS charges a transparent percentage of collections. The percentage, and the definition of “collections” it applies to, are set out in writing before you sign, so the fee moves with your revenue. Your quote depends on volume, payer mix, sites of service, and whether anesthesia or facility billing is in scope.
Who it is for
AMS serves practices, clinics and hospitals nationwide. The GI clients who benefit most tend to be:
- Single-specialty GI practices that own or lease time in an endoscopy center.
- Hospital-affiliated GI groups whose professional-fee billing must be separated from facility billing.
- Multi-location groups with several endoscopy sites and payer contracts, and practices adding a provider.
The scope is the same as on our medical billing services page, applied to GI. Our gastroenterology billing, coding and reimbursement guide covers the rest of the GI code set.
Frequently asked questions
What does a gastroenterology billing service do that a general biller does not?
It applies the endoscopy rules on every claim: screening-to-diagnostic conversion and its modifiers, the diagnostic-versus-surgical edit, the multiple-endoscopy payment rule, and reconciliation of the professional, anesthesia and facility claims.
Do you bill for the ASC and the anesthesia provider as well as the physician?
Yes, where the client contracts for it. The ASC bills its own facility claim and the physician and anesthesiologist bill separately under Part B; when we bill all three, they are built from the same operative note.
What changes for colonoscopy patients on 1 January 2027?
For Medicare, coinsurance on a screening colonoscopy that becomes diagnostic drops from 15 percent to 10 percent for dates of service in 2027 through 2029, per CMS’s MLN Matters MM12656. PT still has to be on the claim for the reduced coinsurance to apply.
Can you take over our credentialing as well as our billing?
Yes. Credentialing and billing are handled by the same team at AMS, so a new provider’s enrollment and first-claim dates are tracked in one place. Scope is on our medical credentialing services page.
Is outsourced GI billing HIPAA compliant?
A billing company is a business associate under HIPAA. We sign a business associate agreement before any protected health information is shared (45 CFR 164.504(e)) and set out in writing which functions are performed where.
Talk to us
If your converted screenings keep pricing as diagnostic, let us look. Book a call with Madison Gardner, request a general medical billing consultation, or start with a free billing analysis of your GI claims. Coding quick-references are in our resources library.