Stanley Tan, MD
Stanley Tan, MD is an Endocrinology, Diabetes & Metabolism Physician in Castro Valley, CA, registered under NPI 1396747721. This provider registers 2 separate taxonomy codes, which usually means they practise across more than one recognised specialty. NPPES records them as a sole proprietor, meaning the practice is not incorporated as a separate legal entity.
Getting there
The practice address on file is 20642 JOHN DR, Castro Valley, CA 94546. We have not yet mapped what surrounds this office — parking, transit, and nearby pharmacies are added as our data collection reaches each location.
Credentials and Medicare
| Licence | State | Specialty |
|---|---|---|
| ME94328 | FL | Endocrinology, Diabetes & Metabolism… primary |
| G23082 | CA | Endocrinology, Diabetes & Metabolism… |
| G23082 | CA | Internal Medicine Physician |
| 2003-00713 | NC | Endocrinology, Diabetes & Metabolism… |
Licences are recorded in 3 states: FL, CA, NC. Providers licensed in several states often practise near a state border or deliver telehealth across state lines.
- Status
- Approved
- Provider type
- Practitioner - Endocrinology
- PAC ID
- 9032105614
Medicare enrolment is recorded as approved under the provider type Practitioner - Endocrinology. This means the provider is enrolled to bill Medicare, though it does not tell you whether they are currently accepting new Medicare patients. Call the office to confirm.
Licensed in 3 states
This provider holds licences in 3 states: California, Florida and North Carolina. The practice address on file is in Castro Valley, CA, but a licence in another state usually means they see patients there too — either at a second location or by telehealth. If the address above is far from you, it is worth calling to ask whether they practise closer to where you live.
- Licence
- G23082
- Specialty
- Endocrinology, Diabetes & Metabolism…
- Licence
- 2003-00713
- Specialty
- Endocrinology, Diabetes & Metabolism…
Licence numbers are self-reported to NPPES at registration. They do not confirm a licence is currently active, in good standing, or valid for the specialty shown — only the state board can tell you that, which is why we link to each one.
What Endocrinology, Diabetes & Metabolism covers
An internist who concentrates on disorders of the internal (endocrine) glands such as the thyroid and adrenal glands. This specialist also deals with disorders such as diabetes, metabolic and nutritional disorders, obesity, pituitary diseases and menstrual and sexual problems. NUCC Health Care Provider Taxonomy, code 207RE0101X
All registered taxonomy codes
This provider registers 4 taxonomy codes. The primary code is what appears on most claims; the others record additional recognised specialties.
| Code | Specialty | Licence | State | |
|---|---|---|---|---|
| 207RE0101X | Endocrinology, Diabetes & Metabolism Physician Endocrinology, Diabetes & Metabolism | ME94328 | FL | primary |
| 207RE0101X | Endocrinology, Diabetes & Metabolism Physician Endocrinology, Diabetes & Metabolism | G23082 | CA | |
| 207R00000X | Internal Medicine Physician | G23082 | CA | |
| 207RE0101X | Endocrinology, Diabetes & Metabolism Physician Endocrinology, Diabetes & Metabolism | 2003-00713 | NC |
The taxonomy records how the provider classifies their own practice. It does not confirm which conditions they currently treat, whether they are accepting new patients, or which insurance they take — call the office for that.
Full NPPES record
An NPI-1 identifies a single person. It stays with the clinician for life, even if they move practice or change state, which is why the address on file can lag behind where they actually work today.
| NPI | 1396747721 valid check digit |
|---|---|
| Entity type | Individual (NPI-1) |
| Enumeration date | Aug 15, 2005 |
| Last updated | Oct 8, 2025 |
| Status | Active |
| Sole proprietor | Yes |
| Credential | MD |
| Practice address |
20642 JOHN DR Castro Valley, CA 94546 (510) 785-5000 |
| Other identifiers |
V7918
· HFMG (FL) 89133MT (NC) PENDING (FL) |
Number check
How the check works, step by step
Every NPI carries a Luhn check digit — the same scheme used on credit cards. CMS prefixes the number with 80840 before computing it, which marks it as a US health identifier.
| Digit | 8 | 0 | 8 | 4 | 0 | 1 | 3 | 9 | 6 | 7 | 4 | 7 | 7 | 2 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Doubled? | — | ×2 | — | ×2 | — | ×2 | — | ×2 | — | ×2 | — | ×2 | — | ×2 |
| Value | 8 | 0 | 8 | 8 | 0 | 2 | 3 | 9 | 6 | 5 | 4 | 5 | 7 | 4 |
Sum = 69 · next multiple of 10 = 70 · check digit = 1 · actual last digit = 1
A valid check digit only means the number is well-formed. It does not mean the provider is licensed, active, or in good standing — those are separate questions answered by the sections above.