Type 1 · Individual ✓ Active NPI ✓ Valid NPI checksum

Clarissa Thannen, RD, LD

Registered Dietitian in Springfield, IL · enumerated 2026 · practices at Siu Physicians & Surgeons, Inc.

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

National Provider Identifier

1558273631

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Registry record

Entity type Individual (Type 1)

Name Clarissa Thannen

Credential RD, LD

Sex Female

Practice address 751 N Rutledge St Ste 1700, Springfield, IL, 62702

Phone (217) 545-8000

Enumeration date Sep 22, 2026

Last updated in NPPES Sep 22, 2026

Taxonomy & licenses

133V00000X Registered Dietitian Dietary & Nutritional Service Providers · License 164025792 (IL) Primary

RD · Registered Dietitian: A nutrition professional credentialed by the Commission on Dietetic Registration. About the RD credential

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

Is NPI 1558273631 active?

Yes, as of the latest NPPES snapshot, NPI 1558273631 is active (record last updated 2026-09-22).

How do I verify Clarissa Thannen's NPI record?

Cross-check NPI 1558273631 against the official CMS registry at npiregistry.cms.hhs.gov. This page mirrors the same public NPPES data with a monthly snapshot.

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Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2026-09-22.