Methodology
How NPIMap turns separate public files into one page per NPI, how relationships are identified, and the rules we follow so every fact can be traced back to its source.
NPI numbers
An NPI is a 10-digit number whose last digit is a check digit computed with the Luhn algorithm (using the health-industry prefix 80840). NPIMap only serves pages for numbers that pass this check, so mistyped NPIs return “not found” instead of an empty page.
How identifiers are connected
No single public file links every identifier, so NPIMap connects them only where a government file lists two identifiers together:
- NPI ↔ Medicare enrollment ID ↔ PAC ID: Medicare Fee-For-Service Public Provider Enrollment.
- Enrollment ↔ CMS Certification Number (CCN): hospital, SNF, home health, hospice, FQHC and RHC enrollment files.
- CCN ↔ facility characteristics and ratings: Provider of Services files and Care Compare, which do not include NPIs.
- Owner associate ID ↔ PAC ID: owners in the All Owners files are identified by PECOS associate ID, the same identifier used as PAC ID for enrolled providers, so an owner that is itself Medicare-enrolled links to its NPI.
- NPI ↔ organization, location and tax-ID group: National Provider Directory.
- Clinician ↔ group practice PAC ID and facility CCN: Care Compare Doctors and Clinicians files.
CCNs are normalized (for example, leading zeros that some files drop are restored). Hospital unit CCNs, which carry
a letter in the third position (such as 24T047, a rehabilitation unit), are connected to their parent
hospital’s CCN (240047).
Relationships and evidence
Each connection on a provider page shows badges naming the evidence behind it. When several sources describe the same connection, the badges are combined and the connection is ranked higher. Lists show the strongest connections first (at most 1,000 per list).
| Badge | What it means |
|---|---|
| Medicare reassignment | The individual has reassigned their right to Medicare payment to the organization, so the organization bills Medicare for their services. This usually reflects employment or a contract, but the file does not say which. |
| Care Compare group | Medicare Care Compare lists the clinician as a member of the organization’s group practice. |
| NPD / NPD (past) | A National Provider Directory practitioner role connects the clinician to the organization. Inactive roles are shown as past. |
| Care Compare affiliation | Care Compare lists the clinician as affiliated with the hospital or facility (matched to the facility’s NPI through its CCN). |
| Same enrollment / Same PAC ID | The NPIs appear on the same Medicare enrollment, or on enrollments with the same PECOS associate control ID. |
| NPD tax ID / NPD member | The organizations share a tax identifier in NPD, or NPD lists an organization affiliation between them. |
| CMS ownership | The facility’s Medicare enrollment discloses the other party as an owner, officer, director or managing party. |
| CMS change of ownership | A Medicare change-of-ownership record lists one as buyer and the other as seller. |
| Provider of Services | Provider of Services files list the certifications as related, parent or unit provider numbers. |
| Name & address match | No shared identifier exists; see matching below. |
Ownership roles are shown as disclosed. Officers, directors and managing employees are listed with ownership because CMS requires their disclosure, but they do not necessarily own any part of the facility.
Name and address matching
Some files share no identifier with NPI records: clinical laboratories (CLIA), dialysis facilities and medical equipment suppliers. NPIMap connects such a record to an organization NPI only when the street number, street name and ZIP code are identical and either
- the organization names are closely similar (after removing words such as “Inc” and “LLC” and standardizing spellings such as “Center”/“Ctr”) and one organization is clearly the best match, or
- exactly one organization at that address has a matching type of care (for example, a dialysis facility and an organization whose primary taxonomy is end-stage renal disease treatment).
These connections carry the “Name & address match” badge and are never used for exclusion or ownership information. We test the rules on facilities where the answer is known because CMS publishes both identifiers:
| Test set | Known CCN–NPI pairs | Matched | Exact NPI | Same legal organization |
|---|---|---|---|---|
| Ambulatory surgical centers | 5,612 | 4,453 | 96.5% | 97.1% |
| Hospitals | 5,945 | 2,123 | 95.0% | 97.5% |
Currently connected: 126,400 CLIA laboratory certificates, 6,050 dialysis facilities and 46,673 medical equipment supplier locations.
Separately, NPPES lets an organization report that it is a subpart of a parent organization, but only by legal name. When exactly one non-subpart organization in the same state has that normalized legal name, the two are linked with an “NPPES parent name” badge.
Exclusions
An OIG exclusion is shown only when the LEIE record contains the provider’s NPI. Most LEIE records have no NPI, and NPIMap never matches exclusions by name, so the absence of a notice does not mean a provider is not excluded. The National Provider Directory’s exclusion flag is shown with that attribution. Always confirm with the OIG.
Names, addresses and specialties
Names, addresses, phone numbers, taxonomy codes, license numbers, other identifiers, other names and endpoints come from the monthly NPPES full replacement file and weekly updates. They are shown as reported; we only change letter case for readability. NPPES records are self-reported and many are not updated regularly, so each page shows the date the provider last updated the record, and Medicare enrollment, Care Compare and NPD addresses are shown alongside it.
Specialty names come from the NUCC Health Care Provider Taxonomy code set. Browse pages use the taxonomy marked as primary, or the first one listed when none is marked.
States and cities
Browse pages use the primary practice location in NPPES. City spellings are grouped so that variants such as “St. Louis”, “St Louis” and “Saint Louis” appear together, labeled with the most common spelling. Providers outside the United States and its territories appear on their NPI pages but not in state browse pages.
Deactivated and replaced NPIs
NPPES lists deactivated NPIs without names or addresses. Their pages answer with HTTP 410 (gone) and are not indexed. When NPPES records a replacement NPI, the old address redirects to the replacement’s page.
Updates
Each source is loaded into a separate build database, checked by automated quality gates (record counts, join rates between files, known reference providers, document integrity) and then published in a single atomic switch, so pages never mix old and new data. Weekly NPPES updates are applied to the affected pages directly. The data sources page lists the exact file and as-of date for every dataset.