Medical and Health Classification Systems Compared

Medical and Health Classification Systems Compared

TL;DR: ICD-10-CM for US billing, ICD-11 for global reporting, LOINC for lab tests, ATC for drugs, MeSH for research. WorldOfTaxonomy connects all of these (and more) - 568K+ health codes across 100+ systems with crosswalk edges between them.

System overview

SNOMED CT and CPT are included as structural placeholders. Full datasets require licenses from SNOMED International and the AMA respectively.

How health systems connect

graph TB
  subgraph Diagnoses["Diagnosis Systems"]
    ICD10CM["ICD-10-CM\n97,606 codes"]
    ICD11["ICD-11 MMS\n37,052 codes"]
    ICD10PCS["ICD-10-PCS\n79,987 codes"]
  end
  subgraph Drugs["Drug Systems"]
    ATC["ATC WHO 2021\n6,440 codes"]
    NDC["NDC\n112,077 codes"]
    RXNORM["RxNorm (skeleton)"]
  end
  subgraph Research["Research & Lab"]
    MESH["MeSH\n31,124 descriptors"]
    LOINC["LOINC\n102,751 observations"]
    NCI["NCI Thesaurus\n211,072 terms"]
  end
  subgraph Clinical["Clinical"]
    SNOMED["SNOMED CT\n(skeleton)"]
    CPT["CPT (skeleton)"]
  end
  ICD10CM <-.-> ICD11
  ICD10CM <-.-> MESH
  ATC <-.-> ICD10CM
  LOINC <-.-> ICD10CM
  SNOMED <-.-> ICD10CM
  NDC <-.-> ATC
  NCI <-.-> MESH
  CPT <-.-> ICD10PCS

ICD-10-CM vs ICD-11: Which to use?

ICD-10-CM (United States)

ICD-10-CM is the US clinical modification of the WHO's ICD-10. It is required for US healthcare billing and reporting.

• 97,606 codes - the most granular diagnosis system in the graph
• Structure: 3-7 character alphanumeric codes (e.g., E11.65 - Type 2 diabetes with hyperglycemia)
• Required by: CMS, US health insurers, HIPAA transactions
• Updated: annually (October 1 each year)

ICD-11 MMS (Global)

ICD-11 is the latest WHO revision, adopted by the World Health Assembly in 2019.

• 37,052 codes with extension codes for additional detail
• Structure: Alphanumeric with cluster and post-coordination
• Status: Official WHO standard since January 2022

When to use which

LOINC - Laboratory and clinical observations

LOINC (Logical Observation Identifiers Names and Codes) is the universal standard for identifying health measurements, observations, and documents.

• 102,751 codes - the largest observation vocabulary
• Use cases: lab test orders and results, clinical documents, patient surveys
• Structure: 5-7 digit numeric codes with check digit
• Required by: US federal health agencies, HL7 FHIR implementations

LOINC does not classify diseases (that is ICD's role). It classifies what was measured or observed. A LOINC code identifies the test, an ICD code identifies the condition.

MeSH - Medical subject headings

MeSH is the controlled vocabulary used for indexing biomedical literature in PubMed/MEDLINE.

• 31,124 descriptors organized in a hierarchical tree
• Use cases: literature search, research categorization, knowledge organization
• Structure: 16 top-level categories branching into specific terms
• Maintained by: US National Library of Medicine

ATC - Drug classification

The Anatomical Therapeutic Chemical (ATC) classification organizes drugs by the organ system they target and their therapeutic properties.

• 6,440 codes across 5 hierarchical levels
• Structure: 7-character codes (e.g., A10BA02 = metformin)
• Levels: Anatomical group, Therapeutic subgroup, Pharmacological subgroup, Chemical subgroup, Chemical substance
• Maintained by: WHO Collaborating Centre for Drug Statistics

graph TD
  A["A - Alimentary Tract\nand Metabolism"] --> A10["A10 - Drugs Used\nin Diabetes"]
  A10 --> A10B["A10B - Blood Glucose\nLowering Drugs"]
  A10B --> A10BA["A10BA - Biguanides"]
  A10BA --> A10BA02["A10BA02\nMetformin"]

Domain-specific health vocabularies

WorldOfTaxonomy includes domain taxonomies for healthcare specialization:

API examples

# Search for a medical term across all systems
curl "https://worldoftaxonomy.com/api/v1/search?q=diabetes&grouped=true"

# Browse ICD-10-CM hierarchy
curl https://worldoftaxonomy.com/api/v1/systems/icd10_cm/nodes/E11/children

# Get ICD-10-CM code detail
curl https://worldoftaxonomy.com/api/v1/systems/icd10_cm/nodes/E11.65

# Browse ATC hierarchy from top level
curl https://worldoftaxonomy.com/api/v1/systems/atc_who_2021/nodes/A10/children

# LOINC system overview
curl https://worldoftaxonomy.com/api/v1/systems/loinc

# Cross-system equivalences for a diagnosis code
curl https://worldoftaxonomy.com/api/v1/systems/icd10_cm/nodes/E11/equivalences

Use cases