LOINC AND SNOMED
Tim Benson
Abies Ltd
Wellcome Trust Sintero Server Project
Cardiff University
Author:
Principles of Health Interoperability HL7 and SNOMED, Springer 2010
OUTLINE
Origins of LOINC
 Origins of SNOMED CT
 Complementary or Competitive

SCOPE OF LOINC

Clinical Laboratory Tests


The test not the result
Clinical observables

“Eye colour”, not “Blue eyes”
Form headings
 Document types
 Assessment scales

ORIGINS OF LOINC
Logical Observation Identifiers Names and Codes
 Designed for use in interoperability
 Clem McDonald

ASTM 1238:88 Standard Specification for
Transferring Clinical Laboratory Data Between
Independent Computer Systems
 HL7 V2.0 1988
 OBX Segment


EU EUCLIDES and OpenLabs projects
HL7 V2 OBX SEGMENT
Turn-round document
 Observable



Code
Value
Code
 Physical quantity

EUCLIDES

European Clinical Laboratory Data Exchange
Standard 1988-1991


Georges De Moor, Gent
6 dimensional classification
LOINC CODES

LOINC Code
Consecutive number + Check digit
 e.g. 12345-9

Short convenient name
 Long common name
 All codes are pre-coordinated to common concept
model
 Six dimensions


slightly different from EUCLIDES
LOINC DIMENSIONS

Component


Property


sample or body part
Scale


point in time or period
System


kind of property measured
Timing


what is being measured
nominal, ordinal, interval or ratio
Method

procedure used to produce the result or other
observation
RELMA
Regenstrief LOINC Mapping Assistant
 LOINC database search
 Map local codes to LOINC codes

PROBLEMS OF LOINC
Complex
 Many similar codes with only small differences

mass concentration v molecular concentration
 anatomical position of pulse or BP


Dimensions are not hierarchical so limits
subsumption testing
GOOD ASPECTS OF LOINC
Completely free
 Does what it claims to do (but no more)
 Fit for purpose
 Easy and quick to add new codes

ORIGINS OF SNOMED CT (1)

SNOMED
CAP committee 1955
 SNOP 1965

topography
 morphology
 etiology
 function (physiology)




SNOMED 1975
SNOMED III 1993
SNOMED RT (Reference Terminology) 1997
ORIGINS OF SNOMED CT (2)

Read Codes

Coded terms in EHR

e.g. “Blue Eyes”
Developed by Abies and James Read for use in GP
computer system 1983-1986
 Purchased by DH in 1990




V2 1990
Version 3 (CTV3) 1996
Used by all GPs in UK (100%)
Basis of payment
 Unsuccessful in other specialties

READ CODE (V1,2) CHAPTERS

Diagnoses


Medication


BNF Chapters a-z
History and physical


ICD Chapters A-Z
Occupations (0), history and symptoms (1), physical
examination findings (2)
Procedures

Diagnostic (3), lab (4), imaging (5), prevention (6),
therapy (7), surgery (8), admin (9)
SNOMED CT
Merger of Read Codes and SNOMED RT
 Reference Terminology


All concepts are in hierarchies (19)
Concepts
 Descriptions (terms)
 Relationships



Defining, qualifying, sub-type, association
Description Logic
PROBLEMS OF SNOMED CT
Much legacy baggage
 Lack of transparency

Lack of free access
 Lack of good web-based tools


Complexity


Post-coordination is not yet a practical proposition
Undefined boundaries

Over-sold as answer to all terminology problems
BENEFITS OF SNOMED CT
Future-proof structure
 Inherently multi-lingual
 Broad coverage

EDUCATION PROBLEM
Few people are competent in both LOINC and
SNOMED
 Clinical terminology is not taught well



One of 186 topics in AMIA Core Curriculum for
Clinical Informatics (JAMIA, 2009)
Formal training is essential

93% of all those who rated themselves as competent
had had more than 3 days formal training in
SNOMED CT (Report for DH, unpublished)
EDUCATION – NEEDS A BLENDED
APPROACH
1.
2.
3.
4.
5.
Learn by doing (assignments and examples)
Face-to-face presentations
Web-based presentations and videos
User guides and books
Pick it up from colleagues
LOINC AND SNOMED CT TOGETHER

Clinical statement consists of:
Narrative text
 Context (who, when , where, etc)
 Observable
 Finding


(Rector A. What’s in a code, MEDINFO 2007)
OBSERVABLE

“Observables” are qualities of patients that are
present in all patients


and whose values or states are determined by
observation
This is what LOINC is designed to code and does
it well
FINDING
Information specific to a particular patient
 Finding = Observable + Value
 Value may be various data types



Physical quantity, code, date, text etc
SNOMED CT is good for Observation Value
Codes
CONCLUSIONS
LOINC and SNOMED CT were originally
designed to do different things
 They are complementary
