Key takeaways
- A screening colonoscopy is billed as screening until the physician finds and removes something. Then the claim changes to a diagnostic or therapeutic procedure, and the coding and patient cost sharing change with it.
- Medicare bills screening with G0105 (high risk) or G0121 (not high risk). When it turns diagnostic, you bill the CPT code for what was done and add modifier PT.
- Medicare does not recognize modifier 33 on colonoscopy or anesthesia. Many commercial payers want 33, PT or neither, so the payer policy decides.
- After a positive stool-based test, Medicare treats the follow-on colonoscopy as screening and wants modifier KX.
Screening vs diagnostic colonoscopy: what changes the claim
A screening colonoscopy is done on a patient with no symptoms to look for polyps or cancer. It is a preventive service, so payers waive or reduce patient cost sharing. A diagnostic colonoscopy is done because of a symptom, a positive test or a known finding. A therapeutic colonoscopy removes something, such as a polyp.
The trouble is that the same visit can start as one and end as another. The patient is booked for screening, the physician finds a polyp and removes it, and the procedure is no longer only screening. The claim has to show that change, or the payer will deny it, pay it wrong or bill the patient the wrong amount.
How Medicare bills it
Medicare uses HCPCS G0105 for screening colonoscopy in a high-risk patient and G0121 for a patient who is not high risk. Frequency limits apply: every 24 months for high risk, and every 10 years for not high risk, or 48 months after a screening flexible sigmoidoscopy.
When a screening colonoscopy turns diagnostic or therapeutic, you stop billing G0105 or G0121. You bill the CPT code for the procedure that was done, such as 45380 for a biopsy or 45385 for snare removal, and append modifier PT. The screening diagnosis goes first and the finding goes second.
| What happened | Medicare coding | Patient cost sharing |
|---|---|---|
| Normal screening, nothing found | G0121 (not high risk) or G0105 (high risk) | None |
| Screening, polyp removed or biopsy taken | CPT for the procedure done, plus modifier PT | Coinsurance applies (see below) |
| Colonoscopy after a positive stool-based test | Screening colonoscopy code with modifier KX | Treated as screening |
| Symptoms or known disease | Diagnostic CPT with the symptom or finding as the diagnosis | Normal diagnostic cost sharing |
The coinsurance phase-down
When a Medicare screening colonoscopy turns diagnostic or therapeutic and carries modifier PT, the patient owes reduced coinsurance. It is 15% for 2023 through 2026, 10% for 2027 through 2029, and 0% from 2030. Tell patients at scheduling that a polyp removal can produce a bill, and what to expect.
Commercial payers and modifier 33
Under the preventive services rules, most commercial plans cover a screening colonoscopy with no patient cost sharing. What they do when it turns diagnostic varies. Some payers ask for modifier 33 on the screening CPT code, some ask for PT, some want a specific diagnosis code order and some pay the whole claim as screening. Medicare does not recognize modifier 33 on colonoscopy or anesthesia, so do not carry it over from commercial claims to Medicare claims.
The safest rule is to keep a one-page policy sheet for each of your top payers that says which modifier and diagnosis order they want, and to check it when a payer updates its policy.
Common colonoscopy billing mistakes
- Billing G0121 or the screening code for the whole visit after a polyp was removed.
- Missing modifier PT on a Medicare claim that turned diagnostic, so the patient is billed the wrong amount.
- Using modifier 33 on a Medicare claim.
- Dropping the screening diagnosis, or putting the finding first, so the payer treats the whole visit as diagnostic.
- Not checking frequency limits before scheduling, so a screening is denied as too soon.
- Billing anesthesia for a screening colonoscopy and a diagnostic one the same way. Anesthesia has its own codes, 00812 for screening and 00811 for other lower intestinal endoscopy, and the payer decides how the status change is shown.
Sources
Medicare screening codes, frequency limits, modifier PT, KX for the follow-on colonoscopy and the coinsurance schedule: Noridian Medicare, Colorectal Cancer Screening. Check your own MAC and each commercial payer for current policy.
Colonoscopy billing FAQ
What is the difference between a screening and a diagnostic colonoscopy?
A screening colonoscopy is done on a patient without symptoms to look for polyps or cancer. A diagnostic colonoscopy is done because of a symptom, a positive test or a known finding. A therapeutic colonoscopy removes something. The claim and the patient cost sharing differ for each.
What is modifier PT on a colonoscopy?
Medicare uses modifier PT when a colonoscopy that started as screening becomes diagnostic or therapeutic. You bill the CPT code for the procedure done and append PT, with the screening diagnosis first and the finding second.
Does Medicare use modifier 33 for colonoscopy?
No. Medicare does not recognize modifier 33 on colonoscopy or anesthesia codes. Some commercial payers do ask for it, so check each payer policy.
What is the coinsurance when a screening colonoscopy turns diagnostic?
For Medicare it is 15% for 2023 through 2026, 10% for 2027 through 2029, and 0% from 2030.
How do you bill a colonoscopy after a positive stool test?
Medicare treats a follow-on colonoscopy after a positive non-invasive stool-based test as a screening service and asks for modifier KX on the screening code.
How often will Medicare pay for a screening colonoscopy?
Every 24 months for high-risk patients, and every 10 years for patients who are not high risk, or 48 months after a screening flexible sigmoidoscopy.