Mary Johnstone
NPI 1639810807 · Physician Assistant · Cambridge, MA
Enrolled with Medicare as Practitioner - Physician Assistant · source: CMS PECOS Public Provider Enrollment (2026.04.01)
Mary Johnstone is a Physician Assistant provider in Cambridge, MA (NPI 1639810807).
Provider details
- NPI number
- 1639810807
- Entity type
- Individual
- Primary specialty
- Physician AssistantPhysician Assistants & Advanced Practice Nursing Providers
- Sex
- Female
- Sole proprietor
- Yes
- License
- 4930 (TN)
Specialties & taxonomies
Physician Assistants & Advanced Practice Nursing Providers
Allopathic & Osteopathic Physicians
Profile Score
A profile completeness & documented-activity index — NOT a quality, outcomes, or patient-satisfaction rating.
- Registry tenure38% of score
4 yrs in NPPES registry
- Profile completeness38% of score
100% of core fields populated
- Practice footprint23% of score
2 documented practice locations
Signals a provider has no public data for (e.g. Medicare claims) are left out of the score entirely — never counted as zero — so providers without that data are not penalized. See the full formula and weights in our methodology.
What this provider prescribes (Medicare Part D)
Top drugs by Medicare Part D claim volume, 2024 · 5 distinct drugs on file.
| Drug | Part D claims (2024) | Beneficiaries |
|---|---|---|
| Peg3350/Sod Sulf,bicarb,cl/Kclbrand: Gavilyte-G | 108 | 105 |
| Peg3350/Sod Sulf,bicarb,cl/Kclbrand: Peg-3350 and Electrolytes | 53 | 53 |
| Colestipol Hcl | 12 | — |
| Omeprazole | 12 | — |
| Pantoprazole Sodium | 11 | — |
Medicare Part D only. These counts cover prescriptions paid through Medicare Part D in 2024 — they do notinclude cash-pay, commercial-insurance, Medicaid, or Part B–administered drugs, and badly undercount high cash-pay categories (e.g. GLP-1 weight-loss, testosterone, and ED medications). Any drug with 10 or fewer claims is omitted by CMS, and beneficiary counts under 11 are suppressed — so a missing drug means no Part D record, never zero. This is a factual claims summary, not an endorsement, not medical advice, and not a consumer report. Source: CMS Medicare Part D Prescribers — by Provider and Drug.
Practice location
Mailing address
Additional practice locations (1)
- 7887 Wolf River BlvdGermantown, TN 38138-1718Phone: (731) 695-9684
Registry dates
- Enumerated
- 2022-04-05
- Last updated
- 2023-05-05
- Certified
- 2023-05-05
Frequently asked questions
- What is Mary Johnstone's NPI number?
- Mary Johnstone's National Provider Identifier (NPI) is 1639810807, a unique 10-digit ID issued by CMS for use in standard healthcare transactions.
- What is Mary Johnstone's specialty?
- Mary Johnstone is listed in the NPPES registry with a primary specialty of Physician Assistant (Physician Assistants & Advanced Practice Nursing Providers).
- Where is Mary Johnstone located?
- Mary Johnstone's practice location on file with NPPES is 1493 Cambridge St, Cambridge, MA 02139-1099.
- What is Mary Johnstone's phone number?
- The practice phone number listed in the NPPES registry for Mary Johnstone is (617) 665-1000.
- Does Mary Johnstone accept Medicare?
- Mary Johnstone is approved to bill Medicare according to CMS PECOS enrollment data (2026.04.01). Confirm current participation with the provider before scheduling.
- Is Mary Johnstone's NPI active?
- Yes — Mary Johnstone's NPI (1639810807) is active in the NPPES registry as of the last update on 2023-05-05.
Source: CMS NPPES Data Dissemination (June 2026). NPI Central is not affiliated with CMS. Data is provided as-is from the public registry.