SNOMED CT - Clinical Terminology¶

Systematized Nomenclature of Medicine - Clinical Terms

SNOMED CT is the most comprehensive and precise clinical health terminology in the world, providing a standardized way to represent clinical information.

Overview¶

Full Name: Systematized Nomenclature of Medicine - Clinical Terms
Concepts: 300,000+ active concepts
Relationships: 1,000,000+ relationships between concepts
System URL: http://snomed.info/sct
Maintained By: SNOMED International
Update Frequency: Biannual (January and July)

Key Features¶

Comprehensive Coverage¶

SNOMED CT covers a wide range of clinical domains:

Clinical Findings: Diseases, symptoms, signs
Procedures: Surgical, diagnostic, therapeutic procedures
Body Structures: Anatomical locations and structures
Organisms: Bacteria, viruses, parasites
Substances: Drugs, chemicals, biological substances
Pharmaceutical Products: Medications and drug products

Polyhierarchical Structure¶

graph TD A[Clinical Finding] --> B[Disease] A --> C[Sign or Symptom] B --> D[Infectious Disease] B --> E[Chronic Disease] D --> F[Viral Disease] D --> G[Bacterial Disease] F --> H[COVID-19] F --> I[Influenza] C --> J[Fever] C --> K[Cough]

Common SNOMED CT Concepts¶

Vital Signs¶

Code	Display Name	Definition
386725007	Body temperature	The measured temperature of the body
271649006	Systolic blood pressure	The maximum arterial pressure during contraction
271650006	Diastolic blood pressure	The minimum arterial pressure during relaxation
364075005	Heart rate	The number of heartbeats per minute
86290005	Respiratory rate	The number of breaths per minute

Common Conditions¶

Code	Display Name	Category
38341003	Hypertension	Cardiovascular
73211009	Diabetes mellitus	Endocrine
195967001	Asthma	Respiratory
13645005	Chronic obstructive pulmonary disease	Respiratory
386661006	Fever	Symptom

Usage Examples¶

In FHIR Observation¶

{
  "resourceType": "Observation",
  "status": "final",
  "code": {
    "coding": [{
      "system": "http://snomed.info/sct",
      "code": "386725007",
      "display": "Body temperature"
    }]
  },
  "valueQuantity": {
    "value": 37.5,
    "unit": "°C",
    "system": "http://unitsofmeasure.org",
    "code": "Cel"
  }
}

In FHIR Condition¶

{
  "resourceType": "Condition",
  "code": {
    "coding": [{
      "system": "http://snomed.info/sct",
      "code": "38341003",
      "display": "Hypertension"
    }]
  },
  "subject": {
    "reference": "Patient/123"
  }
}

Concept Relationships¶

SNOMED CT uses relationships to connect concepts:

Relationship Types¶

IS-A: Hierarchical relationship (subtype)
FINDING-SITE: Anatomical location
CAUSATIVE-AGENT: Etiological agent
ASSOCIATED-MORPHOLOGY: Structural change
PROCEDURE-SITE: Location of procedure

Searching SNOMED CT¶

By Code¶

concept := snomedCT.LookupCode("386661006")
// Returns: Fever

By Description¶

concepts := snomedCT.Search("diabetes")
// Returns: Diabetes mellitus, Diabetic retinopathy, etc.

By Hierarchy¶

children := snomedCT.GetChildren("64572001") // Disease
// Returns: Infectious disease, Chronic disease, etc.

Best Practices¶

Use Specific Concepts

Always use the most specific concept available. For example, use "Type 2 diabetes mellitus" instead of just "Diabetes mellitus".

Post-Coordination

SNOMED CT supports post-coordination (combining concepts), but use pre-coordinated concepts when available for better interoperability.

Versioning

Specify the SNOMED CT version in production systems:

http://snomed.info/sct/900000000000207008/version/20240101

Integration with Other Systems¶

SNOMED CT to ICD-10 Mapping¶

graph LR A[SNOMED CT: 38341003
Hypertension] -->|Maps to| B[ICD-10: I10
Essential Hypertension] C[SNOMED CT: 73211009
Diabetes mellitus] -->|Maps to| D[ICD-10: E11
Type 2 Diabetes]