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Code Systems Overview

Code systems are the foundation of healthcare terminology. They define the concepts, codes, and relationships used to represent clinical information in a standardized way.

What is a Code System?

A code system (also called a terminology or vocabulary) is a collection of concepts with unique codes. Each concept represents a specific clinical idea, such as a disease, procedure, or observation.

Available Code Systems

International Standards

  • SNOMED CT

    Clinical terminology with 300,000+ concepts covering diseases, findings, procedures, and more.

  • LOINC

    Laboratory and clinical observations with 90,000+ codes for tests and measurements.

  • ICD-10

    International disease classification with 70,000+ diagnosis codes.

  • RxNorm

    Medication terminology with 100,000+ drug concepts and relationships.

Bangladesh FHIR Core

The Bangladesh FHIR Core provides country-specific code systems for local healthcare needs:

  • Blood Groups

    8 concepts - ABO and Rh blood group classifications.

  • Religions

    7 concepts - Religious affiliations recognized in Bangladesh.

  • Occupations

    71 concepts - Occupation categories for demographic data.

  • Geo Codes

    1,591 concepts - Complete geographic codes for Bangladesh (divisions, districts, upazilas, municipalities).

  • Medications

    6 concepts - Common medications used in Bangladesh.

  • Vaccines

    10 concepts - Vaccines in Bangladesh immunization programs.

  • Dose Forms

    10 concepts - Pharmaceutical dose forms (tablets, capsules, etc.).

  • Identifier Types

    3 concepts - Types of identifiers (NID, Birth Registration, etc.).

  • Immunization Reaction

    6 concepts - Adverse reactions to immunizations.

  • Immunization Route

    5 concepts - Routes of administration for vaccines.

  • Immunization Site

    5 concepts - Body sites for vaccine administration.

  • Country List

    188 concepts - International country codes for nationality.

Code System Statistics

Category Code Systems Total Concepts
International Standards 4 460,000+
Bangladesh Core 12 1,910
Total 16 461,910+

Code System Structure

graph TD A[Code System] --> B[Concepts] B --> C[Code] B --> D[Display Name] B --> E[Definition] B --> F[Properties] B --> G[Relationships] G --> H[Parent Concepts] G --> I[Child Concepts] G --> J[Related Concepts]

Using Code Systems

In FHIR Resources

{
  "resourceType": "Observation",
  "code": {
    "coding": [{
      "system": "http://loinc.org",
      "code": "8867-4",
      "display": "Heart rate"
    }]
  }
}

With Bangladesh Core

{
  "resourceType": "Patient",
  "extension": [{
    "url": "http://zarishsphere.org/fhir/StructureDefinition/religion",
    "valueCodeableConcept": {
      "coding": [{
        "system": "https://fhir.dghs.gov.bd/core/CodeSystem/bd-religions",
        "code": "1",
        "display": "Islam"
      }]
    }
  }]
}

Code System Comparison

Feature SNOMED CT LOINC ICD-10 Bangladesh Core
Primary Use Clinical terms Lab/Observations Diagnoses Local context
Hierarchy Polyhierarchical Flat Hierarchical Flat
Granularity Very detailed Detailed Moderate Specific
Updates Biannual Biannual Annual As needed
Scope International International International Bangladesh

Best Practices

Choosing the Right Code System

  • Use SNOMED CT for detailed clinical documentation
  • Use LOINC for laboratory results and vital signs
  • Use ICD-10 for diagnosis coding and billing
  • Use Bangladesh Core for local demographic and administrative data

Code System Versions

Always specify the code system version in production systems to ensure consistency.

Multiple Codings

FHIR allows multiple codings for the same concept, enabling cross-system interoperability.

Next Steps