Quick answers
- Does Mark A. Casillas Jr. accept Medicare assignment?
- Yes. Medicare's clinician data says Mark A. Casillas Jr. accepts Medicare assignment (the Medicare-approved amount as full payment for covered services), as of October 2, 2026. Ask the office to confirm before your visit.
- How many Medicare patients does Mark A. Casillas Jr. see?
- In 2024, CMS data shows 166 Original Medicare patients and 440 services for Mark A. Casillas Jr.. This counts Original Medicare only and measures volume, not quality.
- What is Mark A. Casillas Jr.'s NPI number?
- 1245458082. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Medicare activity in 2024
Official CMS public-use data for Mark A. Casillas Jr., data year 2024 (released May 21, 2026). It covers Original Medicare (fee-for-service) patients only, not Medicare Advantage or other insurance. It shows volume, not quality or outcomes. CMS hides any count of 10 or fewer patients.
| Original Medicare patients | 166 |
|---|---|
| Services billed to Medicare | 440 |
| Different services or procedures | 85 |
| Participating Medicare provider | Yes |
| Average age of these patients | 73 |
Most frequent services
- Diagnostic exam of anus using an endoscope (46600)55 services
- Established patient office or other outpatient visit with low level od decision making, if using time, 20 minutes or more (99213)45 services
- Removal of polyps or growths of large bowel using a flexible endoscope with electrical cautery (45384)36 services
- New patient office or other outpatient visit with low level of medical decision making, if using time, 30 minutes or more (99203)36 services
- Diagnostic exam of rectum and lower large bowel using an endoscope (45300)21 services
Chronic conditions among these patients
Share of this clinician’s Original Medicare patients with each condition, as published by CMS (it describes the patients, not the care given).
- High blood pressure75%
- High cholesterol75%
- Arthritis50%
- Cancer (breast, colorectal, lung, prostate, endometrial or leukemia/lymphoma)34%
- Ischemic heart disease30%
- Anxiety30%
Hospitals where Mark A. Casillas Jr. works
Medicare's Facility Affiliation Data lists Mark A. Casillas Jr. at these hospitals (updated October 2, 2026). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians. Star rating and emergency services: Hospital General Information (CMS), data updated October 26, 2026.
- University Health System, IncKnoxville, TN · Acute Care Hospital · Medicare rating: 4 of 5 stars · Emergency services: listed by Medicare · CCN 440015
- Wellmont Holston Valley Medical CenterKingsport, TN · Acute Care Hospital · Medicare rating: 2 of 5 stars · Emergency services: listed by Medicare · CCN 440017
Practice locations
Addresses where Mark A. Casillas Jr. is enrolled with Medicare (CMS data updated October 2, 2026).
- 1924 Alcoa HwyKnoxville, TN 37920
- 1930 Alcoa HwyKnoxville, TN 37920
- 1930 Alcoa Hwy 235Knoxville, TN 37920 (865) 305‑4670
Group practices
Medicare enrollment lists Mark A. Casillas Jr. as a member of this group (CMS data updated October 2, 2026).
- University Health System, Inc.522 clinicians in the group
Specialties
Find other Colorectal Surgery (Proctology) doctors in Tennessee →
Other colorectal surgeons in Knoxville
Clinicians with the same Medicare primary specialty in Knoxville, TN — not a recommendation.
Other clinicians in University Health System, Inc.
Medicare enrollment lists these clinicians in the same group practice — not a recommendation.
Clinician information
| Credential | MD |
|---|---|
| Graduation year | 2006 (20 years since medical school) |
| Gender (as listed) | Male |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| NPI (National Provider Identifier) | 1245458082 |
| Corrections | Report an error or suggest an update → |
Most corrections must be made at the source: clinicians update their NPI Registry record (NPPES) and their Medicare enrollment (PECOS); this page follows the next data release.
Sources
- Facility Affiliation Data — Centers for Medicare & Medicaid Services (CMS), data updated October 2, 2026, retrieved October 29, 2026
- Hospital General Information — CMS, data updated October 26, 2026, retrieved November 13, 2026
- National Downloadable File (Doctors and Clinicians) — CMS, data updated October 2, 2026, retrieved October 29, 2026
- Medicare Physician & Other Practitioners - by Provider — CMS, data year 2024, released May 21, 2026; Medicare Physician & Other Practitioners - by Provider and Service
- NPI Registry — U.S. Department of Health and Human Services (NPPES), the clinician’s official record
- Medicare Care Compare — official Medicare tool to look up clinicians