Type 1 · Individual ✓ Active NPI ✓ Valid NPI checksum

Mrs. Grethel Leff, ASW

Clinical Social Worker in Pleasanton, CA · enumerated 2010.

Data current as of Jul 13, 2026 · sourced from CMS NPPES

National Provider Identifier

1851692842

Verified

See something wrong? Report a correction

Registry record

Entity type Individual (Type 1)

Name Mrs. Grethel Leff

Credential ASW

Sex Female

Practice address 5354 Case Ave, # 920, Pleasanton, CA, 94566

Phone (925) 895-2661

Enumeration date Nov 8, 2010

Last updated in NPPES Dec 13, 2010

Taxonomy & licenses

1041C0700X Clinical Social Worker Behavioral Health & Social Service Providers · License 28974 (CA) Primary

What is an NPI number?

A National Provider Identifier (NPI) is a unique 10-digit number that CMS assigns to every U.S. healthcare provider and organization under HIPAA. Type 1 NPIs identify individual providers; Type 2 NPIs identify organizations. The NPI appears on insurance claims, prescriptions, and credentialing paperwork, and never changes, even if the provider moves or changes specialty.

Read the full guide → Validate an NPI →

Frequently asked questions

What specialty is Grethel Leff?

Grethel Leff is registered in NPPES with the primary taxonomy of Clinical Social Worker. The taxonomy code describes the provider's classification and area of specialization for claims and credentialing.

Is this the official NPI registry?

No. NPI Portal is a private site built on public CMS NPPES data. The official registry is npiregistry.cms.hhs.gov, operated by CMS.

Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2010-12-13.