Colonoscopy clinicians in O'Fallon, Illinois
CMS lists 12 clinicians with a primary specialty of Gastroenterology, Internal Medicine, Family Practice, or General Practice who have billed Medicare for at least one colonoscopy and practice in O'Fallon, Illinois (details below).
Colonoscopy volume
| Clinician | Colonoscopies billed | Percentile rank |
|---|---|---|
| Peter Kim, MD | 269 | 94% |
| Naeem Aslam, MD | 126 | 73% |
| Michael Ansstas, MD | 114 | 69% |
| Kenechukwu Chudy-Onwugaje, MD | 99 | 64% |
| Amit Mori, MD | 68 | 49% |
| Ishaan Vohra | 54 | 41% |
| Mike Giacaman, MD | 33 | 28% |
| Praveen Sampath, MD | 33 | 28% |
| Robert Garner, DO | 20 | 19% |
| Saadullah Khan, MD | 20 | 19% |
| Stuart Weisman, MD | 13 | 15% |
| Scott Morrison, MD | 1-10 | 13% or below |
Sorted by the number of colonoscopies billed to Medicare, highest first, not by quality or skill. CMS suppresses counts between 1 and 10 to protect patient privacy and publishes the range instead.
Understanding CMS Data
CMS's "Colonoscopy" category combines specific billing codes for colonoscopy to calculate the number of times each clinician billed Medicare for a "Colonoscopy." These include screening colonoscopy, diagnostic colonoscopy, and colonoscopy with biopsy or polyp removal. CMS's list also includes flexible sigmoidoscopy and laparoscopic appendectomy, so a clinician's count may include those procedures. CMS counts one procedure per patient per day, so a colonoscopy that included both a biopsy and a polyp removal counts once. CMS reports only procedures that clinicians billed to Original Medicare and Medicare Advantage. Therefore, CMS's procedure volume data does not include procedures that clinicians may have performed on patients who have other health care coverage (e.g., commercial insurance, self-pay, or the VA). Billing variation and coding errors can also affect CMS's data. Therefore, the number of procedures that CMS reports for a clinician may be higher or lower than the actual number of colonoscopies a clinician performed during the reporting period. Lastly, only clinicians with a primary specialty of Gastroenterology, Internal Medicine, Family Practice, or General Practice (as reported to Medicare) are presented.
Source: Centers for Medicare & Medicaid Services (August 18, 2026 release).