NPPES file of Aug 9, 2026

Chelsea Joy Thomsen, M.D., M.S.P.H

Internal Medicine Physician · San Francisco, CA

Chelsea Joy Thomsen, M.D., M.S.P.H is an internal medicine physician with a practice address in San Francisco, California, and NPI 1003227927, issued on May 13, 2014. Check the license (California A170520, as entered in NPPES) on the Medical Board of California; the Medicare figures below come from public CMS files.

Record from CMS NPPES, file of Aug 9, 2026 · Medicare files 2024 · method · Verify with CMS →

NPPES recordNPPES file of Aug 9, 2026
1003227927
Name
Chelsea Joy Thomsen
Credential
M.D., M.S.P.H
Primary taxonomy
Internal Medicine Physician 207R00000X
License numbers
A170520 CA
50576 AZ
Self-reported in NPPES; status is on the state search
Practice location
2 W Portal Ave, San Francisco, CA 94127
Phone
(415) 291-0480
Enumerated
May 13, 2014
Record last updated
Mar 14, 2025
Fax
(415) 252-7176
Medicare enrollment
Enrolled (PECOS I20211213001196); accepts Medicare assignment
Medical or professional school
University Of Arizona College Of Medicine, 2014
Telehealth
Offers telehealth (CMS)
Entity
Type 1 · individual
Public record from CMS NPPES (open it on the CMS NPI Registry). Enrollment, assignment, school and telehealth: CMS Doctors and Clinicians file, Aug 2026. A record is not a license: verify it with the state board.
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8 nearest internal medicine physician records → All 17,696 in California → Look up another NPI →

Also registered at 2 W Portal Ave

A shared address usually means a shared clinic or building; it does not show who employs whom.

  1. Katherine Clarke, CRNPNurse Practitioner1659071801
  2. Petia Kremen, MDInternal Medicine Physician1861570418
  3. Victoria Lau, D.O.Family Medicine Physician1336482298
  4. Nina Metsovaara, NP-C, FNPFamily Nurse Practitioner1356706634
  5. David Sly, DOFamily Medicine Physician1255387148
  6. Anna Tellefsen, NPPediatric Nurse Practitioner1982342770

Verify Chelsea Joy Thomsen in five checks

  1. 1IdentityNPI record in CMS NPPESNPI lookupConfirmed in NPPES
  2. 2LicenseActive license and public ordersMedical Board of California
    Search for license A170520    Check the board
  3. 3Other statesLicenses and actions elsewhereDocInfo (FSMB)Not checked
  4. 4ExclusionsMedicare and Medicaid bansHHS-OIG exclusion listNot checked
  5. 5CertificationBoard certificationABMS AOA NCCPA AANPNot checked
Open the California license search

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94% fewer Medicare Part D claims than the average internal medicine physician in 2024

177 Medicare Part D claims for 34 beneficiaries, against an average of 3,176 among the 108,855 providers of this specialty who prescribed in Part D. Brand-name drugs were 12% of claims.

  1. Chelsea Thomsen177
  2. Specialty average3,176

Most prescribed

  1. Atorvastatin Calcium22 claims
  2. Levothyroxine Sodium16 claims
  3. Losartan Potassium12 claims

Source: CMS Medicare Part D Prescribers by Provider and Drug, 2024 (data.cms.gov). Part D covers prescriptions for Medicare patients only; drugs with fewer than 11 claims are not published.

Bills Medicare through one group practice

  1. One Medical Group IncSan Francisco, CA

Source: CMS Doctors and Clinicians National Downloadable File (the group practices a clinician bills Medicare through) (data.cms.gov).

Chelsea Joy Thomsen among 17,696 internal medicine physician records in California

Chelsea Joy Thomsen, M.D., M.S.P.H is one of 17,696 internal medicine physician records with a practice address in California. 79% of them appear in a Medicare file (Part D prescribing, MIPS, Open Payments or Medicare group billing); this one does. Its NPI, issued in 2014, is newer than 74% of them.

  • NPI issued2014 · 74% of these records are older, 24% newer
  • In a Medicare fileYes · 79% of these records are
  • In the CMS Doctors and Clinicians fileYes · 63% of these records are
  • Graduated2014 · median 2004 among the 11,065 with a school on file
  • Record last updated2025 · 61% of these records were not updated in five years or more

Source: CMS NPPES, file of Aug 9, 2026, every record with primary taxonomy 207R00000X and a California practice address; Medicare files: CMS Part D Prescribers 2024, MIPS 2023, Open Payments 2024, Doctors and Clinicians (data.cms.gov).

1,318 internal medicine physician records list a practice address in San Francisco

They are 1,318 of the 38,143 NPPES records with a practice address in San Francisco, and 17,696 internal medicine physician records in California.

All 17,696 in California → Every provider in San Francisco → Internal Medicine Physician nationwide →

The 8 internal medicine physician records with the nearest ZIP codes

  1. Richard Chin, M.D.San Francisco, CA 941271588825640
  2. Petia Kremen, MDSan Francisco, CA 941271861570418
  3. Joel Lopez, M.D.San Francisco, CA 941271376679910
  4. Neil Solomon, M.D.San Francisco, CA 941271861598450
  5. Mary Jean Stempien, M.D.San Francisco, CA 941271073734521
  6. Silva Yuen, MDSan Francisco, CA 941271336201755
  7. John Hall, MDSan Francisco, CA 941251861423600
  8. Ross Quinn, MDSan Francisco, CA 941241871082602

Common questions

What is Chelsea Joy Thomsen, M.D., M.S.P.H's NPI number?

Chelsea Joy Thomsen, M.D., M.S.P.H's National Provider Identifier (NPI) is 1003227927, issued on May 13, 2014. An NPI identifies a provider in billing; it is not a license.

Where is Chelsea Joy Thomsen, M.D., M.S.P.H located?

The NPPES record lists a practice address at 2 W Portal Ave, San Francisco, CA, 94127. Phone: (415) 291-0480. Providers update this record themselves, so call before visiting.

How can I verify Chelsea Joy Thomsen, M.D., M.S.P.H's license?

NPPES lists California license number A170520, as entered by the provider. Search the Medical Board of California at https://www.mbc.ca.gov/License-Verification/default.aspx. The NPPES record confirms identity only; the state search shows license status, expiration and public orders.

How much does Chelsea Joy Thomsen, M.D., M.S.P.H prescribe under Medicare Part D?

In 2024, Chelsea Joy Thomsen, M.D., M.S.P.H had 177 Medicare Part D claims for 34 beneficiaries; the average among internal medicine physician prescribers was 3,176. Part D covers Medicare prescriptions only.

Source: CMS National Plan and Provider Enumeration System (NPPES), file of Aug 9, 2026 (NPPES files on CMS.gov); NUCC Health Care Provider Taxonomy. Medicare files from data.cms.gov. An NPI identifies who bills; it is not a license.

Written with AI tools from the named public files; every figure is computed from those files (how it is made).

Figures on PlainDoctor are read from the federal files each page names (CMS NPPES, Medicare Part D, MIPS, Open Payments; the HHS-OIG exclusion list only as counts) and from Census population estimates, with the file date shown beside them. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of Aug 9, 2026.