Colonoscopy CPT codes 45378 to 45385: screening vs diagnostic

45378 is diagnostic colonoscopy with no intervention. 45380 adds biopsy, 45384 adds removal by hot forceps or bipolar cautery, and 45385 adds removal by snare technique. Screening colonoscopies use G0105 for high-risk patients and G0121 for average-risk patients. When a screening becomes therapeutic, append modifier PT to the CPT code so the patient’s cost sharing is handled correctly.

Colonoscopy coding is a good example of a technically simple procedure wrapped in a genuinely complicated benefit structure. The clinical decisions are made in ten minutes. The billing consequences of those decisions run for months.

The core code set

Code	Service
45378	Diagnostic colonoscopy, with or without collection of specimens by brushing or washing
45380	Colonoscopy with biopsy, single or multiple
45381	Colonoscopy with submucosal injection
45382	Colonoscopy with control of bleeding
45384	Colonoscopy with removal of lesions by hot biopsy forceps or bipolar cautery
45385	Colonoscopy with removal of lesions by snare technique
45388	Colonoscopy with ablation
G0105	Screening colonoscopy, individual at high risk
G0121	Screening colonoscopy, individual not meeting high risk criteria

Two structural points. The therapeutic codes are alternatives to 45378, not additions to it; you do not bill 45378 alongside 45385 for the same procedure. And where different techniques are used on different lesions in the same session, multiple codes can be appropriate with the correct modifier, but the same technique on multiple lesions is one code regardless of how many polyps were removed.

The screening versus diagnostic problem

This is the entire billing story for colonoscopy, and it is a benefit question rather than a coding question.

A screening colonoscopy is a preventive service. The patient has no signs, no symptoms, and no relevant history driving the study, and preventive benefits typically waive patient cost sharing. A diagnostic colonoscopy investigates a symptom, a positive stool test, or a known finding, and normal cost sharing applies.

The intent at the time the procedure is scheduled determines the category. A patient who arrives for screening and turns out to have a polyp did not retrospectively arrive for a diagnostic procedure. This is exactly what modifier PT exists to handle.

• Modifier PT: append to the CPT code when a colorectal cancer screening service converts to a diagnostic or therapeutic procedure. It tells the payer the encounter began as screening, which protects the patient’s cost-sharing treatment even though a therapeutic code is now being billed.
• Modifier 33: identifies a preventive service, used with commercial payers where PT is not the applicable convention.

Omitting PT on a converted screening is one of the most consequential small errors in gastroenterology billing. The claim usually pays. The patient receives an unexpected bill for a procedure they were told would be free, and the resulting complaint, adjustment, and write-off cost more than the coding correction would have.

A separate and increasingly common trap is the follow-up colonoscopy after a positive non-invasive stool test. Whether that study is treated as screening or diagnostic has been the subject of policy change, and payer interpretations have not been uniform. Confirm the current position with the specific payer rather than assuming, because this is high volume and getting it wrong systematically is expensive.

Anesthesia, facility, and the other claims on the same case

A single colonoscopy can generate three or four claims: the physician’s professional claim, the facility or ambulatory surgery center claim, the anesthesia claim, and pathology on any specimen obtained. They have to agree with one another.

Where they disagree, the denials look mysterious. Anesthesia billed against a screening code when the physician billed diagnostic, or pathology with a diagnosis that contradicts the endoscopist’s indication, both produce rejections that are hard to trace back because the failing claim is not the one that caused the problem. Reconciling linked claims across a case is a specific discipline and it belongs in claim scrubbing rather than in post-denial detective work.

Frequency, intervals, and eligibility

Screening colonoscopy carries frequency limitations that vary by risk category, generally a longer interval for average-risk patients and a shorter one for high risk. A study performed inside the interval denies for frequency regardless of clinical reasoning.

The prior procedure date is therefore a scheduling input, not a billing input. Verifying benefit category, prior procedure date, and applicable interval before the appointment is the single highest-yield control available in this specialty, and it sits in eligibility verification. Where the study also requires authorization, that belongs in prior authorization services.

2026 payment context

Colonoscopy codes are not time-based, which means they fell within the scope of the 2.5% efficiency adjustment CMS finalized for 2026 on the work RVUs and intra-service time of non-time-based services. The practice expense reallocation also applies, so the professional payment differs by setting more than it did in 2025. Because most colonoscopy volume is performed in ambulatory surgery centers and hospital outpatient departments rather than offices, that reallocation generally works against this specialty on the professional claim.

Verify your own figures through the CMS Physician Fee Schedule lookup, and note that facility payment for the case runs on separate systems with their own annual updates.

Where correctly coded therapeutic colonoscopies are being short-paid or bundled, that is recoverable through denial management and underpayment recovery. For the coding oversight that keeps screening conversions handled correctly at volume, see medical coding services.

Frequently asked questions