Full checklist › Code-system mapping gaps

Code-system mapping gaps High-risk silent loss

Crosswalking SNOMED CT, ICD-10-CM, RxNorm, LOINC, and CVX between EHRs is where meaning silently shifts: version drift, one-to-many ambiguity, RXCUI≠NDC, retired concepts, and codes landing in the wrong terminology slot.

Anchored to:

• SNOMED CT — SNOMED International; US distributed by NLM (US National Release Center) (US Edition releases Mar 1 / Sep 1.)

• ICD-10-CM — CDC / NCHS (FY2026 effective Oct 1, 2025. Guidelines maintained by the four Cooperating Parties (AHA, AHIMA, CMS, NCHS).)

• RxNorm — NLM (NIH) (Monthly full + weekly updates; no annual edition. RXCUI is a normalized concept, not an NDC.)

• LOINC — Regenstrief Institute (Released ~2x/yr. Confirm current build on Downloads page.)

• CVX (vaccine codes) — CDC (IIS) (Continuously maintained (Active/Inactive status).)

• UMLS / Metathesaurus — NLM (NIH) (CUI is not a guarantee of semantic equivalence at your needed granularity.)

General IT / operational guidance — not medical, legal, or compliance advice. This is a data-integrity validation checklist for EHR migration. Standards and versions revise; verify every citation and version against the live owner page and confirm requirements with your EHR vendor and your organization's compliance/HIM team before acting.

What to validate

Local/proprietary codes never bound to a standard terminology will migrate as orphaned codes or free text — inventory and remediate them before cutover.
Version drift: map historical data using the terminology release IN EFFECT WHEN RECORDED, then forward-map. Codes get retired/inactivated/re-parented across releases.
One-to-many / many-to-one crosswalk ambiguity (GEMs, SNOMED↔ICD): auto-picking the 'first' target silently changes meaning — flag ambiguous maps for human review.
RXCUI ≠ NDC: RXCUI is a normalized concept; NDC is packaging/manufacturer-specific (one RXCUI → many NDCs). Preserve both as separate related fields.
Honor retired SNOMED concepts' historical-association refsets (SAME AS / REPLACED BY) — don't drop them.
Validate codes land in the correct terminology slot (labs→LOINC not ICD; problems→SNOMED/ICD not LOINC).
UMLS CUI is not a guarantee of semantic equivalence at your needed granularity — don't treat a CUI match as a clean map.

Get the runnable validation toolkit →All 7 failure modes

Not medical advice. IT/operational guidance for EHR data-migration validation, anchored to official HL7/FHIR, ONC/ASTP, HIPAA (eCFR), and code-system sources. Last verified 2026-06-22. Verify versions and requirements with your vendor and compliance team. Some outbound links may be referral links.