Gastroenterology Medical Billing Services
Gastroenterology billing turns on one distinction more than any other: was this colonoscopy screening or diagnostic? The answer changes the code, the patient's cost share, and whether your front desk has an angry phone call to handle.
Codes this specialty bills most
| Code | Description | Watch for |
|---|---|---|
| 45378 | Diagnostic colonoscopy, flexible, with or without collection of specimen by brushing or washing | The base diagnostic code. Not for screening on an average risk patient. |
| 45380 | Colonoscopy with biopsy, single or multiple | When performed during a screening, modifier PT or 33 preserves the screening benefit. |
| 45385 | Colonoscopy with removal of lesion by snare technique | Same modifier rule. Billing this without it is where surprise patient bills come from. |
| G0121 | Colorectal cancer screening, colonoscopy on individual not meeting high risk criteria | Medicare screening code for average risk patients. |
The denials this specialty sees
The screening conversion is the whole game. A patient books a screening colonoscopy, having been told preventive care is covered at no cost. A polyp is found and removed. The claim goes out as a therapeutic procedure with no modifier, and the patient receives a bill for a deductible they were promised they would not owe.
That is not usually a denial. It is a correctly processed claim producing a bad outcome, and it costs you the patient relationship. Modifier 33 for commercial payers and PT for Medicare exist to prevent it.
Frequency limits are the second pattern. Screening intervals are fixed by payer policy and a claim submitted early denies outright. Check the last screening date before scheduling, not after billing. See CO-151.
Third is anesthesia. Most payers now cover monitored anesthesia care for routine endoscopy, but a few still require documented risk factors. Where that applies, the anesthesia claim denies while the endoscopy pays, and it is easy to miss.
Our coding review checks screening modifiers before submission, which is the only point at which this is fixable without a phone call to the patient.
Payer notes
Medicare uses G0105 and G0121 for screening colonoscopy and modifier PT when a screening becomes diagnostic. Commercial payers generally use the CPT codes with modifier 33. Applying the Medicare convention to a commercial claim, or the reverse, produces a patient balance that should not exist.
Screening interval rules differ between Medicare and commercial plans, and between commercial plans.
Common questions
The patient was told the colonoscopy was free and got a bill. What happened?
Almost always a missing modifier. A screening that becomes therapeutic keeps its preventive benefit when modifier 33 or PT is applied. Without it the claim processes as a diagnostic procedure and the deductible applies. It is correctable by rebilling.
When do we use modifier 33 rather than PT?
PT is the Medicare convention. Modifier 33 is used for commercial payers. Check the individual payer policy, because there are exceptions and the cost of getting it wrong lands on the patient.
How do we avoid frequency denials?
Verify the last screening date and the patient's risk category before the procedure is scheduled. High risk patients qualify more often, but the documentation has to establish the risk.
See what your claims are leaving behind
Send us a month of remittance data and we will tell you what it says: which codes are being denied, how much of it is recoverable, and how long your money is sitting in A/R. It takes about a week and there is nothing to sign.