HCPCS Code G0104: Colorectal cancer screening flexible sigmoidoscopy

Key Takeaways

HCPCS Code G0104 reports colorectal cancer screening by flexible sigmoidoscopy for average-risk Medicare Part B beneficiaries aged 45 and older.

Medicare covers G0104 once every 48 months with no patient cost-sharing when billed correctly as a preventive service.

Screening-to-diagnostic conversion is a high-error area: if polyps or lesions are found and the procedure becomes diagnostic, cost-sharing rules change and modifier selection must reflect that shift.

Pabau’s claims management software supports billing workflows including frequency tracking, ICD-10 pairing, and modifier logic for preventive service codes like G0104.

Colorectal cancer is the second leading cause of cancer-related death in the United States, yet most cases are preventable when caught early. That prevention gap sits squarely in your billing workflow. When G0104 claims are submitted with the wrong ICD-10 code, an incorrect modifier, or a missed frequency check, Medicare denies the claim and the patient loses access to a no-cost screening.

HCPCS Code G0104 is the specific Medicare code for colorectal cancer screening by flexible sigmoidoscopy. Getting it right means understanding not just the code itself, but the coverage rules, documentation requirements, and common denial patterns that trip up even experienced billers. This guide covers all of it, including the 2025-2026 fee schedule rates, required ICD-10 pairings, modifier rules, and what happens when a screening converts to a diagnostic procedure.

HCPCS Code G0104: definition and official code description

Claims management software that handles preventive service codes needs to start from the correct source definition. According to the Centers for Medicare and Medicaid Services (CMS), HCPCS Code G0104 carries the official descriptor: “Colorectal cancer screening; flexible sigmoidoscopy.”

G0104 is a Level II HCPCS G-code, maintained by CMS rather than the American Medical Association. G-codes cover services not described in the CPT code set, primarily Medicare-specific preventive and diagnostic services. This code is exclusive to Medicare Part B and cannot be used for commercial payer claims.

Medicare coverage criteria for G0104

Medicare Part B covers flexible sigmoidoscopy for colorectal cancer screening under National Coverage Determination (NCD) 210.3. Coverage applies when the following eligibility conditions are all met:

• The patient is enrolled in Medicare Part B
• The patient is aged 45 or older (CMS lowered the minimum screening age from 50 to 45, effective 2023, to align with updated USPSTF recommendations; verify current eligibility under the applicable MAC LCD)
• The patient is classified as average risk for colorectal cancer (no personal history of colorectal cancer, adenomatous polyps, inflammatory bowel disease, or a family history that qualifies as high risk)
• The required frequency interval has been met (see frequency limitations below)

When these criteria are satisfied and HCPCS Code G0104 is filed with a correct ICD-10 diagnosis code, the service is covered as a Medicare preventive benefit. The patient pays no deductible or coinsurance. That no-cost-sharing status disappears if the procedure converts from screening to diagnostic during the encounter. Billers must track that conversion carefully because the modifier and cost-sharing rules change on the same claim.

Reviewing the Medicare compliance checklist for primary care before submitting G0104 claims can help practices confirm eligibility verification steps are built into the workflow, not left to individual staff memory.

Frequency limitations for G0104

Medicare reimburses HCPCS Code G0104 once every 48 months for average-risk beneficiaries. Claims submitted before the 48-month window has elapsed are denied on frequency grounds. The table below shows how G0104 frequency compares with related colorectal screening codes.

2025-2026 Medicare reimbursement rates for HCPCS Code G0104

Medicare reimburses G0104 under the Physician Fee Schedule (PFS), with rates varying based on place of service. Facility rates apply when the procedure is performed in a hospital outpatient department (HOPD) or ambulatory surgical center (ASC). Non-facility rates apply to office-based settings. Geographic adjustments through local GAF (Geographic Adjustment Factor) multipliers mean actual payment varies by MAC jurisdiction.

Use the CMS Physician Fee Schedule lookup tool to retrieve the current national and locality-adjusted rates for G0104 in your jurisdiction. The table below reflects approximate 2025-2026 national rates; always confirm current figures directly with CMS before submitting claims.

Facility rates are lower because the facility receives a separate payment directly from Medicare. Non-facility rates are higher to compensate the practice for overhead costs. Submitting a facility POS code when the procedure was performed in an office setting (or vice versa) is one of the leading causes of underpayment and claim adjustment requests on G0104 claims.

ICD-10 diagnosis codes required for G0104 billing

Every G0104 claim requires a valid ICD-10-CM diagnosis code to establish medical necessity for the screening. The two most commonly paired codes are Z12.11 (encounter for screening for malignant neoplasm of colon) and Z12.19 (encounter for screening for other malignant neoplasms of digestive organs). According to multiple AAPC coding resources, these are the standard pairings for average-risk colorectal cancer screening.

Note that specific ICD-10 code requirements may vary by MAC LCD. Always verify the required pairing against your jurisdiction’s current LCD before submitting. The table below lists the primary diagnosis codes and the clinical contexts in which each applies.

When polyps or lesions are found and removed during the encounter, additional ICD-10 codes reflecting those findings may be required alongside the screening code. A clean pre-procedure workflow with digital intake and documentation forms can capture the patient’s risk factors and prior screening history before the procedure, reducing the chance of a wrong diagnosis code pairing at claim submission.

Modifiers for HCPCS Code G0104

Modifier selection for G0104 is one of the most error-prone parts of the billing workflow. Three modifiers are regularly encountered, each serving a distinct purpose. Applying the wrong one, or omitting a required one, is a direct path to denial.

The PT modifier is specifically designed for the screening-to-diagnostic conversion scenario and is where most modifier-related denials occur. When a polyp is found and biopsied or removed during a sigmoidoscopy that began as a G0104 screening, the claim should reflect the conversion. Verify current CMS and MAC guidance before asserting universal modifier applicability, as payer-specific rules can vary.

G0104 billing guidelines: step-by-step workflow

Consistent claim approval on G0104 comes from a repeatable pre-claim workflow. These steps incorporate HIPAA-compliant documentation practices to keep billing aligned with CMS requirements. HIPAA-compliant documentation practices in your billing process protect both the practice and the patient throughout the claims lifecycle.

1. Verify Medicare Part B enrollment and eligibility: Confirm active Part B coverage via HIPAA 270/271 eligibility transaction before scheduling. Note the plan details and any supplement or Advantage plan that may affect billing.
2. Confirm patient risk classification: Document in the medical record whether the patient is average risk or high risk. For G0104, the patient must be average risk. High-risk patients qualify for G0105 (colonoscopy), not G0104.
3. Run a frequency check: Verify the date of the patient’s last qualifying sigmoidoscopy or colonoscopy claim in their Medicare history. G0104 cannot be billed within 48 months of the prior G0104 claim.
4. Select the correct ICD-10-CM code: Use Z12.11 for standard average-risk colon screening. Add secondary codes for relevant family history if documented.
5. Assign the place of service code: Use POS 11 for office settings (non-facility rate), POS 22 for hospital outpatient, POS 24 for ASC. The POS must match the actual service location.
6. Apply the correct modifier(s): Add Modifier 33 for a clean preventive service claim. If the procedure converts to diagnostic, document the conversion and apply Modifier PT on the appropriate claim line.
7. Submit and monitor: File the claim electronically and track the remittance advice for any denial codes. Frequency denials (CO-119) and modifier errors are the most common issues on G0104.

Documentation requirements for G0104

The medical record must support every element of the G0104 claim. Using medical forms for healthcare practices that prompt providers to capture the required fields at the point of care reduces post-procedure documentation gaps. Required documentation includes:

• Patient’s age and date of birth confirming eligibility (45 or older)
• Documented risk classification (average risk) with supporting clinical rationale
• Procedure report describing the flexible sigmoidoscopy findings
• Physician attestation that the procedure was performed for colorectal cancer screening
• Any findings (polyps, lesions, biopsies) that triggered a screening-to-diagnostic conversion, with documentation of the conversion and associated modifier change
• Informed consent for the procedure

Maintaining structured clinical documentation also supports clinical compliance documentation requirements across the practice, particularly when claims are selected for post-payment audit by a MAC or the OIG.

Simplify your HCPCS billing workflow

Pabau's claims management software helps gastroenterology and primary care practices track frequency rules, match ICD-10 pairings, and apply correct modifiers for preventive service codes like G0104. Book a demo to see how it works in practice.

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Common denial reasons for G0104 and how to avoid them

Most G0104 denials are preventable. The billing errors behind them repeat across practices precisely because they are not caught in the pre-submission workflow. Good patient data security in billing workflows also ensures that verification steps are logged and traceable, which matters during payer audits.

Related HCPCS and CPT codes for colorectal cancer screening

G0104 is one code in a broader family of colorectal cancer screening codes. Using the right code depends on procedure type, patient risk level, and whether the screening converts to a diagnostic. EHR systems for primary care billing can help link the appropriate procedure code to patient risk flags automatically, reducing manual code selection errors.

Use the PGM Billing HCPCS lookup tool or the CrossCoder code crosswalk tool to verify current code status and ICD-10 pairings for each of these codes before submitting claims.

CPT codes 45330 and 45378 cover diagnostic (not screening) sigmoidoscopy and colonoscopy. When a G0104 screening converts to a diagnostic procedure, the claim typically transitions to the appropriate CPT code with Modifier PT appended to signal the screening origin. The distinction affects patient cost-sharing and reimbursement rates.

How practice management software simplifies G0104 billing

Manual frequency tracking, ICD-10 pairing, and modifier selection for preventive service codes like G0104 create the conditions for the exact errors that generate denials. Billing workflow features in practice management software address each of these failure points systematically rather than relying on individual staff to remember the rules on each claim.

Pabau’s claims management software supports GI and primary care billing teams with structured claim workflows. For practices managing G0104 volume, the key workflow benefits include:

• Eligibility verification integration: Real-time Medicare Part B eligibility checks before the procedure date, with claims history accessible to confirm the 48-month frequency window
• ICD-10 pairing templates: Pre-built code pairings that default to Z12.11 for average-risk colorectal screening, reducing the risk of a symptom code being selected instead
• Modifier logic support: Procedure-specific modifier templates that prompt coders to apply Modifier 33 for preventive services and flag when a diagnostic conversion modifier (PT) is required
• Structured documentation capture: Digital forms that prompt clinicians to document patient risk classification, informed consent, and procedure findings at the point of care
• Audit trail for compliance: Timestamped documentation supporting post-payment audit responses, aligned with practice management workflows across the full billing cycle

Practices running high volumes of Medicare preventive service claims benefit most from these automations. A frequency denial on G0104 cannot be passed to the patient, so every prevented denial is direct revenue recovery.

Conclusion

G0104 denials are almost always preventable. The 48-month frequency rule, the Z12.11 ICD-10 pairing, and the Modifier 33 / PT distinction account for the vast majority of claim rejections on this code. Getting those three elements right on every claim is the baseline.

Pabau’s digital forms and structured billing workflows help GI and primary care practices build those rules into the process itself, so the right code, the right modifier, and the right diagnosis pairing are defaults rather than decisions. To see how the claims workflow handles HCPCS Code G0104 and other preventive service codes in practice, book a demo with the Pabau team.

Continue your research

Need to verify Medicare coverage eligibility for preventive services? HIPAA-compliant documentation in medical offices covers how to structure patient records to support Medicare preventive service claims.

Managing billing across a primary care or GI practice? Key features in practice management software outlines the workflow tools that reduce claim errors across high-volume billing environments.

Want to reduce post-payment audit exposure? Clinical compliance documentation practices explains how structured documentation workflows protect practices during Medicare audits.

Frequently Asked Questions