Howard Guan, M.D.
Howard Guan, M.D. is a Glaucoma Specialist (Ophthalmology) Physician in San Marcos, CA, registered under NPI 1134427636. This provider registers 2 separate taxonomy codes, which usually means they practise across more than one recognised specialty.
Getting there
The practice address on file is 340 RANCHEROS DRIVE SUITES 164/166, San Marcos, CA 92069. 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 |
|---|---|---|
| A119766 | CA | Ophthalmology Physician |
| A119766 | CA | Glaucoma Specialist (Ophthalmology)… primary |
This provider holds licence A119766 issued in CA. A licence number in NPPES reflects what was filed at registration — it does not confirm the licence is still active today.
- Status
- Approved
- Provider type
- Practitioner - Ophthalmology
- PAC ID
- 4385868256
- Enrollment ID
- I20150724011344
Medicare enrolment is recorded as approved under the provider type Practitioner - Ophthalmology. Being enrolled means the provider can bill Medicare; it does not tell you whether they are currently accepting new Medicare patients. Call the office to confirm.
What Glaucoma Specialist covers
An ophthalmologist who specializes in the treatment of glaucoma and other disorders related to increased intraocular pressure and optic nerve damage. This specialty involves the medical and surgical treatment of these conditions. NUCC Health Care Provider Taxonomy, code 207WX0009X
All registered taxonomy codes
This provider registers 2 taxonomy codes. The primary code is what appears on most claims; the others record additional recognised specialties.
| Code | Specialty | Licence | State | |
|---|---|---|---|---|
| 207W00000X | Ophthalmology Physician | A119766 | CA | |
| 207WX0009X | Glaucoma Specialist (Ophthalmology) Physician Glaucoma Specialist | A119766 | CA | primary |
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 | 1134427636 valid check digit |
|---|---|
| Entity type | Individual (NPI-1) |
| Enumeration date | Mar 7, 2011 |
| Last updated | Oct 21, 2025 |
| Status | Active |
| Sole proprietor | No |
| Gender | Male |
| Credential | M.D. |
| Practice address |
340 RANCHEROS DRIVE SUITES 164/166 San Marcos, CA 92069 (760) 598-0400 Fax (760) 290-7044 |
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 | 1 | 3 | 4 | 4 | 2 | 7 | 6 | 3 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Doubled? | — | ×2 | — | ×2 | — | ×2 | — | ×2 | — | ×2 | — | ×2 | — | ×2 |
| Value | 8 | 0 | 8 | 8 | 0 | 2 | 1 | 6 | 4 | 8 | 2 | 5 | 6 | 6 |
Sum = 64 · next multiple of 10 = 70 · check digit = 6 · actual last digit = 6
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.