NPI registry status
Active
2026 NPPES data Internal Medicine Physician NPI 1366411555 MD
Verify on CMS → Mark Shields, MD
Internal Medicine Physician in Laguna Hills, California.
This profile is drawn from the federal National Provider Identifier Registry (CMS NPPES), which lists more than 7 million U.S. healthcare providers - including 174,792 in Internal Medicine Physician, and covers specialty classification, practice address, and Medicare Part D prescribing data when reported. According to CMS, every field reflects the provider's official federal registration, see our methodology.
Federal data, no proprietary rating.
We show these CMS records as-is - no composite score, no star rating, no editorial opinion layered on top.
Prescribing volume
8K
Medicare Part D claims · 586 beneficiaries · Internal Medicine Physician avg: 3K
Generic prescribing
91%
generic claims · 8% brand-name · higher generic rates reduce patient out-of-pocket costs
MIPS score
81.9/100
▼ 2 pts below national avg 83.5 · Above neutral
Source: CMS Medicare Part D Prescriber Public Use File, 2024
What the federal data shows
Mark Shields, MD reported a CMS MIPS final score of 81.9/100 - below the 83.5 national average - and filed 7,598 Medicare Part D claims in 2024.
- 81.9/100
- MIPS score · -2 vs avg
- 8K
- Part D claims, 2024
- 91%
- generic prescribing
- Likely
- board-certified (heuristic)
Every figure on this page comes straight from federal CMS records (NPPES, Medicare Part D, MIPS, Open Payments) - no proprietary rating or editorial opinion is applied.
Federal trust snapshot
What official records show about Mark Shields, MD
Federal records show an active NPI with both Medicare prescribing volume and a measured CMS quality score — objective registry data, not patient reviews.
- Verified
NPI registry status
Active listing in the CMS National Provider Identifier Registry (NPI 1366411555), first enumerated 03/17/2006.
Source: CMS NPPES
- Reported
Medicare Part D participation
Filed 7,598 Medicare Part D prescription claims in the 2023 CMS public use file — indicates active Medicare prescribing participation.
Source: CMS Part D Prescriber PUF
- Reported
CMS quality reporting (MIPS)
Reported a CMS MIPS final score of 81.9/100 in the Quality Payment Program — a federal quality measure, not a patient review.
Source: CMS Quality Payment Program
- Reported
Board certification signal
Heuristic suggests board-certified status based on ABMS-eligible specialty taxonomy plus active CMS participation signals — not a direct ABMS verification.
- Reported
Hospital affiliations
2 CMS Care Compare hospital affiliations on record — practice footprint from the Doctors and Clinicians file.
Source: CMS Care Compare
- State context
State board disciplinary context
California statewide board action statistics are published annually — these figures describe aggregate state activity, not Mark Shields, MD's individual license status. Verify directly with the state medical board.
Source: MBC annual report 2023
- Not in federal data
Individual sanction lookup
PlainDoctor does not publish per-provider disciplinary determinations. Confirm current license and any individual actions through the state medical board or FSMB verification service.
Source: State medical board / FSMB
This trust snapshot summarizes only what appears in federal CMS/NPPES public records. It is not a composite score, star rating, patient review, or clinical recommendation. PlainDoctor never fabricates reviews or AggregateRating schema.
Compare Shields with other Internal Medicine Physician providers
Same primary specialty, same federal CMS NPPES roster.
All 60 Internal Medicine Physician providers in Laguna Hills, CA →
Also enrolled in California
- Dr. Jacob Aaron, MD San Francisco, CA
- Dr. Alistair Aaronson, MD Stanford, CA
- Dr. Jose Abad., MD Sacramento, CA
- Dr. Donna Abare, MD Oakland, CA
- Marce Abare Scotts Valley, CA
- Dr. Samuel Abarte, M.D. Chula Vista, CA
Other specialties in Laguna Hills: Behavior Technician (301) · Marriage & Family Therapist (176) · Physical Therapist (103) · Addiction (Substance Use Disorder) Counselor (63)
CMS NPPES provider registry desk
NPI 1366411555 · Internal Medicine Physician
NPI-10 · ENUM-LEGACY · TAX-MEGA · MIPS-INLINE · RX-MID · BOOK-MID · PHOTO-FINISH
- NPI-10 1366411555
- ENUM-LEGACY 2006
- TAX-MEGA 175K Internal Medicine
- MIPS-INLINE 81.9/100
- RX-MID 7,598
- BOOK-MID 20,403 in California
- PHOTO-FINISH Amil Patel, MD · ±0.0
MIPS final-score neighbourhood
Same-specialty nationwide peers by CMS final score, not geographic proximity
- Shields · this p…
Shields · this provider
81.9 MIPS pts
- Amil Patel, MD ·…
Amil Patel, MD
81.9 MIPS pts
- Thomas Hansson, …
Thomas Hansson, M.D.
81.9 MIPS pts
- Uzoamaka Nwaogwu…
Uzoamaka Nwaogwugwu, MD
81.9 MIPS pts
- Lloyd Webster, M…
Lloyd Webster, M.D.
81.9 MIPS pts
What this shows Nearest measured MIPS peers for this NUCC specialty (2023 performance year).
Mark Shields, MD's MIPS score vs every measured U.S. clinician
CMS Merit-based Incentive Payment System (MIPS) final score, 2023, the federal quality measure. Clinicians whose score CMS assigned without scoring any category are excluded.
82 ≥ 32nd percentile 32% of 454,083 measured providers are in lower value bands
Each bar is a band; taller bars hold more measured providers. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
The percentile is a conservative whole-score-point band: it counts only measured clinicians in lower score bands. A CMS MIPS metric is not a recommendation or a clinical-quality rating by PlainDoctor. See methodology § corpus placement.
Source CMS Merit-based Incentive Payment System (MIPS) · 2023
Where Mark Shields, MD sits
This provider among internal medicine physician peers
Across the 34,612 internal medicine physician providers who report both Medicare Part D prescribing and a MIPS quality score, Mark Shields, MD writes more Part D claims than 88% of them and scores higher on MIPS quality than 35% - placing this provider in the high-volume, lower-quality quadrant. Volume reflects patient-panel size and specialty, not quality; the two axes are independent.
Each dot is one internal medicine physician peer from a representative sample of 60; the gold marker is Mark Shields, MD. Source: CMS Medicare Part D Prescriber data and the CMS Merit-based Incentive Payment System, 2023.
✓
Board certification likely (heuristic, not verified)
Mark Shields, MD practices in an ABMS-board-eligible specialty and shows active CMS Medicare participation + MIPS quality reporting + 2 hospital affiliations - signals consistent with board-certified status. For verified board certification, see CertificationMatters.org (the official ABMS public lookup).
What does the federal data show about Mark Shields, MD?
Near national averagePrimary specialty
Internal Medicine Physician
Medicare Part D claims
7,598 173% vs specialty avg
MIPS final score
81.9/100 1.6 pts vs avg
Specialty distribution in California
How Internal Medicine Physician compares to other specialties among California providers
Medicare quality performance, MIPS
Mark Shields, MD's 2023 MIPS final score plotted against the Internal Medicine Physician national average
- MIPS Final Score
- 81.9/100
- vs 83.5 national avg · 2023 performance year
How MIPS and board certification work
The Merit-based Incentive Payment System (MIPS) scores providers 0–100 across four performance categories: Quality, Cost, Promoting Interoperability, and Improvement Activities, weighted under 42 CFR §414.1380. Reporting is voluntary for many small practices, so absence of a MIPS score is not a quality signal.
Board certification through an ABMS or AOA member board signals voluntary post-licensure examination plus continuous Maintenance of Certification cycles. Verify any individual provider's status through certificationmatters.org (ABMS) or osteopathic.org (AOA).
Practice Address
Provider Details
| NPI | 1366411555 |
|---|---|
| Specialty | Internal Medicine Physician |
| Credentials | MD |
| Gender | Male |
| NPI Issued | 03/17/2006 |
CMS Quality Score (MIPS)
Merit-based Incentive Payment System (MIPS) scores from CMS, 2023 performance year.
81.8568
Final Score
Measured-score avg: 83.5
79.5972
Quality
66.5921
Cost
92
Promoting Interoperability
Reporting: Individual
Hospital and facility affiliations
Facilities where Mark Shields, MD bills Medicare from. Star ratings (1-5) are CMS Hospital Compare's "Hospital overall rating" - a composite of mortality, readmission, patient experience, safety, timely care, and efficient use of medical imaging measures. Source: CMS Care Compare.
Healthcare Partners Affiliates Medical Group
Laguna Hills, CA
Saddleback Medical Group Inc
Laguna Hills, CA
Affiliations sourced from CMS Doctors and Clinicians National Downloadable File; hospital ratings from CMS Hospital General Information dataset (cross-referenced by facility name + state).
License & disciplinary context - California MBC 2023 annual report
Aggregate state board data only, NOT a determination of any individual provider's status. The figures below describe statewide disciplinary activity across all ~150K California medical licensees in 2023 - they are NOT specific to Mark Shields, MD. To verify Mark Shields, MD's current license status, search the MBC public license lookup directly, or check the Federation of State Medical Boards (FSMB) verification service.
576
Total board actions, California 2023
Across 556 cases
3.84
Actions per 1,000 licensees
California statewide rate
probation
Most common action type
186 cases
MBC publishes annual disciplinary statistics as part of public-record reporting under each state's Administrative Procedure Act. See the full breakdown by action type and year on the California disciplinary trends page. Cross-checked against FSMB U.S. Medical Regulatory Trends.
Brand vs generic prescribing mix · Generic-heavy
Mark Shields, MD - brand share 8.0%
Internal Medicine Physician average
8% brand-name claims vs 91% generic, on 7,598 2024 Medicare Part D claims.
The federal Medicare Part D Generic Dispensing Rate national benchmark sits near 90% generic / 10% brand for primary-care prescribers, per CMS Office of the Actuary 2024 estimates. Higher brand share is common in specialty prescribing where generic equivalents are not available.
Medicare Part D Prescribing Data
CMS Medicare Part D prescriber-level data for calendar year 2024.
7,598
Total Claims
$424K
Total Drug Cost
586
Medicare Beneficiaries
Prescribing Breakdown
- 30-Day Fills
- 17,176.333
- Total Day Supply
- 494,167
- Brand vs Generic
- 8% brand / 91% generic
- Brand Drug Cost
- $313K
- Generic Drug Cost
- $109K
- Opioid Claims
- 246 (3.2% rate)
- Antibiotic Claims
- 331
Patient Demographics
- Average Patient Age
- 79.9 years
- Avg HCC Risk Score
- 1.48
- Gender Split
- 53% female / 47% male
Top Prescribed Drugs (Medicare Part D)
Top drugs by claim count for calendar year 2024. Based on Medicare Part D data only.
What Mark Shields, MD prescribes most
Top Medicare Part D drugs by claim count, 2024
- Atorvastatin Calcium
Atorvastatin Calcium
453 claims
- Losartan Potassium
Losartan Potassium
256 claims
- Amlodipine Besylate
Amlodipine Besylate
251 claims
- Levothyroxine Sodium
Levothyroxine Sodium
242 claims
- Pantoprazole Sodium
Pantoprazole Sodium
217 claims
- Rosuvastatin Calcium
Rosuvastatin Calcium
205 claims
- Hydrocodone-Acetam… 174
Hydrocodone-Acetaminophen
174 claims
- Metformin Hcl 170
Metformin Hcl
170 claims
| Drug | Claims |
|---|---|
| Atorvastatin Calcium | 453 |
| Losartan Potassium | 256 |
| Amlodipine Besylate | 251 |
| Levothyroxine Sodium | 242 |
| Pantoprazole Sodium | 217 |
| Rosuvastatin Calcium | 205 |
| Hydrocodone-Acetaminophen Hydrocodone/Acetaminophen | 174 |
| Metformin Hcl | 170 |
| Lisinopril | 162 |
| Simvastatin | 151 |
* Counts below 11 are suppressed by CMS for patient privacy. Generic names shown where available from CMS Part D data.
Internal Medicine Physician Overview
How Mark Shields, MD fits within the Internal Medicine Physician landscape nationally.
174,792
Internal Medicine Physician Providers in US
56
States with Internal Medicine Physician
2,785
Avg Claims per Provider
Mark Shields, MD's 7,598 claims are above the specialty average of 2,785.
Nationwide Internal Medicine Physician peers with similar MIPS or enrollment year
Two federal-record peer sets for Shields, both outside California so the neighborhoods are not geographic containment.
Similar MIPS final score
Nearest same-specialty clinicians by CMS MIPS final score (81.9 here).
Same NPPES enumeration year (2006)
Same-specialty clinicians who entered the NPI registry in the same calendar year, outside this state.
Nearby Internal Medicine Physician Providers in California
Other clinicians with the same primary specialty enrolled in California, drawn from the same CMS NPPES roster as Shields.
One of 20,403 Internal Medicine Physician providers enrolled in California, 11 are shown on this page.
Dr. Alexander Abary
MD
Long Beach, CA
Dr. Luba Abascal
MD
San Francisco, CA
Dr. Michael Abate
MD
Sacramento, CA
Dr. Wali Abawi
D.O.
Joshua Tree, CA
Hazel Abaya
Thousand Oaks, CA
Compare Internal Medicine Physician nationally: see state-by-state distribution →
Frequently Asked Questions
What is Mark Shields, MD's specialty? ▼
Mark Shields, MD specializes in Internal Medicine Physician and practices in Laguna Hills, California. Credentials: MD.
How much does Mark Shields, MD prescribe under Medicare Part D? ▼
In 2024, Mark Shields, MD wrote 7,598 Medicare Part D claims totaling $424K in drug costs for 586 beneficiaries.
What is Mark Shields, MD's Medicare quality score? ▼
Mark Shields, MD has a CMS MIPS Final Score of 81.9/100 (Quality: 79.6, Cost: 66.6). The average MIPS Final Score across the 454,083 clinicians with at least one published category score is 83.5; clinicians whose score CMS assigned without scoring any category are excluded from that average. Source: CMS Merit-based Incentive Payment System (MIPS) 2023.
Where is Mark Shields, MD located? ▼
Mark Shields, MD is located at 24221 CALLE DE LA LOUISA, Laguna Hills, CA, 92653. Phone: (949) 588-8700.
What is Mark Shields, MD's NPI number? ▼
Mark Shields, MD's National Provider Identifier (NPI) is 1366411555, issued on 03/17/2006.
Does Mark Shields, MD prescribe more brand-name or generic drugs? ▼
Mark Shields, MD's prescribing is 8% brand-name and 91% generic drugs by claim count, with $313K in brand drug costs.
Does Mark Shields, MD prescribe opioids? ▼
Yes, Mark Shields, MD had 246 opioid claims in 2024 with an opioid prescribing rate of 3.2%.
How many Internal Medicine Physician providers are there in the US? ▼
There are 174,792 Internal Medicine Physician providers across 56 states in the US. The average Internal Medicine Physician provider writes 2,785 Medicare Part D claims per year.
What drugs does Mark Shields, MD prescribe most often? ▼
Based on 2024 Medicare Part D data, Mark Shields, MD's most frequently prescribed drugs include Atorvastatin Calcium, Losartan Potassium, Amlodipine Besylate. This reflects Medicare Part D prescriptions only and does not include commercial insurance or other payer types.
Does Mark Shields, MD accept Medicare? ▼
Mark Shields, MD appears in CMS Medicare data with 7,598 Part D claims and 586 Medicare beneficiaries in 2024. Contact the provider's office directly to confirm current Medicare enrollment and accepted plans.
How can I verify Mark Shields, MD's credentials? ▼
Mark Shields, MD's NPI is 1366411555 with credentials MD. You can verify this through the NPPES NPI Registry, check state medical board records, and confirm board certification through the ABMS or AOA.
Data Sources
View source datasets and methodology notes
- Provider Directory
- CMS National Plan and Provider Enumeration System (NPPES), download.cms.gov/nppes, updated monthly. Contains NPI, specialty, credentials, and practice location.
- Specialty Classification
- NUCC Health Care Provider Taxonomy (nucc.org), the industry standard for classifying provider specialties in Medicare and Medicaid billing.
- Prescribing Data
- CMS Medicare Part D Prescriber Public Use File (2024). Includes claims, drug costs, beneficiaries, and opioid prescribing rates.
- Quality Performance
- CMS Merit-based Incentive Payment System (MIPS) - 2023 performance year.
- Limitations
- Provider data is self-reported to CMS. Prescribing data reflects Medicare Part D only and does not include commercial insurance, Medicaid, or cash prescriptions. Claims below 11 beneficiaries are suppressed by CMS for privacy.
See our complete data methodology for details on how we collect and process government data.
Data as of August 2026 (NPPES) / 2024 (Medicare Part D). Source: Centers for Medicare & Medicaid Services (CMS).
Disclaimer: Data from CMS NPPES and Medicare Part D. PlainDoctor does not rate or rank providers. Provider information is self-reported and may not be current. Always verify information directly with the provider. About · Methodology
Every figure on PlainDoctor is rendered directly from the federal CMS NPPES registry, Medicare Part D, MIPS, and Open Payments records, no number is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of August 2026.