HCPCS G0121: Screening Colonoscopy, Not at High Risk
G0121 is the Medicare code for a screening colonoscopy on a patient who does not meet the high-risk criteria. It is payable once every 119 months after the month of the last screening colonoscopy, and a patient who is at high risk is billed on G0105 instead.
Written by Salman Saeed, CEO and Co-Founder · Reviewed by a Certified Medical Coder · Last reviewed October 2026In short: G0121 follows a 10-year frequency limit under 42 CFR 410.37(g), shortened to 47 months after a screening sigmoidoscopy and waived for a colonoscopy that follows a positive stool or blood-based test. It stops being the right code the moment the physician takes a biopsy or removes a lesion, because billing switches to the diagnostic code with PT.
What Does G0121 Report?
G0121 is defined in the HCPCS file as "Colorectal cancer screening; colonoscopy on individual not meeting criteria for high risk". Medicare added it for services on or after July 1, 2001. Under 42 CFR 410.37(a)(3), high risk means a close relative with colorectal cancer or an adenomatous polyp, familial adenomatous polyposis, hereditary nonpolyposis colorectal cancer, a personal history of polyps or colorectal cancer, or inflammatory bowel disease. Anyone else is billed on G0121.
In the October 2026 fee schedule file (RVU26D) G0121 has status A, a 000 global period, a work RVU of 3.18 and a multiple procedure indicator of 2, and a G0121-53 row exists at half the values. Its MUE is 1 per date of service, a policy edit with an anatomic rationale.
How Often Does Medicare Pay for G0121?
Once every 119 months for a patient who is not at high risk. The eCFR text of 42 CFR 410.37(g)(1) says payment may be made after at least 119 months have passed following the month of the last screening colonoscopy.
| Last screening test | Next G0121 payable | Source |
|---|---|---|
| Screening colonoscopy | After at least 119 months following that month | 410.37(g)(1) |
| Screening flexible sigmoidoscopy | After at least 47 months following that month | 410.37(g)(3) |
| Positive stool or blood-based test, then colonoscopy | No frequency limit, billed with KX | 410.37(k); Claims Processing Manual ch. 18, s60.2 |
| Patient at high risk | G0105, after at least 23 months | 410.37(g)(2) |
Chapter 18 counts from the month after the test. Its own barium enema example starts the count in February for a January test and makes the patient eligible again 47 months later. Medicare's Common Working File checks age and frequency on every colorectal screening claim (section 60.2.1).
A screening colonoscopy on March 12, 2016 starts the count in April 2016. The 119th month ends in February 2026, so a G0121 on March 1, 2026 is the first payable date. One earlier, in February 2026, denies for frequency.
What Changes If the Physician Finds a Polyp?
Stop billing G0121 and bill the colonoscopy code for the biopsy or removal with modifier PT. Chapter 18, section 60.2, says the diagnostic procedure "along with modifier -PT should be billed and paid rather than HCPCS G0121". The HCPCS file defines PT as a colorectal cancer screening test converted to a diagnostic test or other procedure. The code choices are on CPT 45385 and CPT 45378.
The deductible is waived on a converted exam. Coinsurance under section 122 of the Consolidated Appropriations Act of 2021 is 15% for 2023 through 2026, 10% for 2027 through 2029, and zero from 2030. Sedation with G0500 or 99153 carries modifier 33 on a screening exam and only PT after conversion. The full conversion rules are on gastroenterology billing.
How Does G0121 Appear on the Claim?
On the CMS-1500, Item 24D carries G0121 with KX or 53 as needed, Item 24G carries 1 and Item 24B is 24 for an ambulatory surgery center, or 22 or 19 for a hospital outpatient department. Modifier 53 marks an interrupted exam; the facility claim uses 73 or 74 instead.
Hospitals bill on the institutional claim. Chapter 18, section 60.6, lists bill types 12X, 13X, 22X, 23X and 85X for the colonoscopy codes, with the revenue code that fits a surgical procedure. Critical access hospitals under payment Method II bill the professional part under revenue code 096X, 097X or 098X and the facility part under 075X.
Medicare pays G0121 at the rate of the diagnostic colonoscopy 45378, and no deductible or coinsurance applies to a true screening. In an ASC it is on Addendum AA with payment indicator A2, payment based on the OPPS relative weight and the same rate as 45378.
Where Do KX, 53 and the Setting Go on a G0121 Claim?
The screening colonoscopy line carries G0121 in Item 24D with KX or 53 as needed, 1 unit in Item 24G and a pointer in Item 24E to the screening diagnosis. Item 24B shows the setting, and Item 24A the date. On a facility claim the code is in FL 44, the date in FL 45 and units in FL 46 under the revenue code in FL 42.
RVU26D gives G0121 status A and a 000 global, and the MUE table allows 1 per date with indicator 2.
Example: A 62-year-old has a screening colonoscopy on 10/18 with no findings. The line is G0121, pointer A (Z12.11), 1 unit, $720.00. If a polyp is removed, the code changes to the polypectomy code, and billing G0121 beside it draws a bundling denial under CO-97.
Why Is G0121 Denied?
| CARC | What X12 says | What usually causes it |
|---|---|---|
| 119 | The benefit maximum for this time period or occurrence has been reached | A prior screening colonoscopy inside the 119 months, or a sigmoidoscopy inside 47 |
| 97 | The benefit is included in the payment for another service already adjudicated | G0121 billed with 45378 or a polypectomy code for the same exam |
| 4 | The procedure code is inconsistent with the modifier used | PT, KX or 33 used on the wrong line |
| 151 | The information submitted does not support this many or this frequency of services | More than 1 unit on a date of service |
| 11 | The diagnosis is inconsistent with the procedure | A symptom diagnosis on a screening line |
If these denials keep coming back, our denial management team can work them.
Related Codes
- Physician Fee Schedule relative value files, RVU26D (October 2026) · CMS
- Medicare NCCI Medically Unlikely Edits, practitioner and outpatient hospital tables, effective 10-01-2026 · CMS
- ASC payment rates and addenda, October 2026 Addenda AA and DD1 · CMS
- Medicare Claims Processing Manual, Chapter 18: Preventive and Screening Services · CMS
- 42 CFR 410.37 Colorectal cancer screening tests: Conditions for and limitations on coverage · eCFR
- HCPCS quarterly update, October 2026 alpha-numeric file · CMS
- Claim Adjustment Reason Codes · X12
- Medicare Claims Processing Manual, Chapter 26: Completing and Processing Form CMS-1500 Data Set · CMS
- Place of service code set · CMS
- Medicare Claims Processing Manual, Chapter 25: Completing and Processing the Form CMS-1450 Data Set · CMS
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Common Questions
Straight answers from the team that does the work.
Ask a billing lead directly. A 20-minute call, Monday to Friday, 9am to 5pm Eastern.
01When do I use G0121 for a screening colonoscopy?
Use it for a Medicare screening colonoscopy on a patient who is not at high risk, with no symptoms and no earlier abnormal finding. Use G0105 for a high-risk patient. If a biopsy or removal happens, bill the diagnostic colonoscopy code with modifier PT instead of G0121.
02How often can G0121 be billed?
Once every 119 months after the month of the last screening colonoscopy, per 42 CFR 410.37(g)(1). Counting starts the month after the last exam. A positive stool or blood-based test followed by a colonoscopy billed with KX is not subject to that limit.
03What is the limit after a screening sigmoidoscopy?
A patient not at high risk who had a screening flexible sigmoidoscopy can have G0121 only after at least 47 months have passed following the month of that sigmoidoscopy. 42 CFR 410.37(g)(3) and Chapter 18, section 60.2, both state the rule.
04Does G0121 have a deductible or coinsurance?
No, when the exam stays a screening. Chapter 18, section 60.1.1, says no deductible or coinsurance applies to G0121. If it converts to a diagnostic exam, the deductible is waived and coinsurance is 15% for 2026 and 10% for 2027 through 2029.
05What modifier goes on G0121?
KX when the colonoscopy follows a positive non-invasive stool-based test, which also lifts the frequency limit. Modifier 53 marks an interrupted exam on the professional claim. Modifier 33 goes on sedation with G0500 or 99153, and PT is for the converted diagnostic code, not G0121.
Screening Colonoscopies Denied for Frequency?
We check the last screening date and the PT and KX modifiers before the claim goes out.