Understanding SNOMED-CT for Healthcare Applications

1. SNOMED Clinical Terms (Snomed CT) – the language for healthcareA presentation for the KIDDM Mashup, 17th September 2007 Ian Herbert Vice Chair BCS Health Informatics Forum With grateful acknowledgements to Dr David Gain of NHS CFH

2. Why do we need Snomed-CT? • To enable consistent representation & retrieval of clinical info: • about individual patients • in knowledge sources, e.g. drug formularies & guidelines • To avoid a combinatorial explosion of the terms needed • To provide a flexible set of classifications of terms • Need a terminology that can be extended quickly & indefinitely • This necessary (but may not be sufficient) for: • analysing patient information, e.g. for mgmnt & research • automated decision support, e.g. for safe prescribing • semantic interoperability between care providers & systems □

3. Dictionary of Clinical Concepts Health Lexicon Thesaurus of Terms What is SNOMED CT? A conceptual classification A controlled clinical vocabulary • SNOMED CT is a terminological resource that can be implemented in software applications to represent clinically relevant information reliably and reproducibly □

4. Why not use ICD10 or OPCS4? • Not not rich enough (or intended) for patient records • No facility to combine expressions to clarify meaning • ‘emergency’ + ‘thoracotomy’ • ‘recurrent’ + ‘IGTN’ + ‘left’ + ‘great toenail’ • Updates too slow (every 10 years for ICD) • SNOMED CT can respond reasonably quickly to • changes in the wider field of medicine • changes in local policy • individual requests for additions • and will never be complete □

5. What’s wrong with free text? • Free text is an extremely valuable and flexible way of recording details about individual circumstances, but… • The meaning may be ambiguous, & open to misinterpretation • Its meaning is not available for computation, e.g. • it can’t automatically be analysed for audit or payment • it can’t direct care pathways • it can’t trigger automatic warnings about allergic reactions or interactions □

6. Documentation in electronic records Reporting Decision support Summaries Clinical audit Administrative / management information Billing & reimbursement Aggregation functionality Epidemiology Resource management Research How is the information used? Direct care Indirect Care

7. One concept, many names • Some of the descriptions associated with ConceptID 22298006: • • Fully Specified Name: Myocardial infarction (disorder)DescriptionID 751689013 • • Preferred term: Myocardial infarctionDescriptionID 37436014 • • Synonym: Cardiac infarctionDescriptionID 37442013 • • Synonym: Heart attackDescriptionID 37443015 • • Synonym: Infarction of heartDescriptionID 37441018

8. Avoiding ambiguity • To a neurologist • Cord compression means Spinal cord compression • To a midwife • Cord compression means Umbilical cord compression • Transmission and sharing of information requires consistency of terminology – and its use □

9. Will the computer limit what I can say? • More concepts • 400,000 health care concepts • More descriptions • 1,000,000 clinical terms • More information • 1,500,000 semantic relationships • Contextual modification of expressions • possible, Family history of, planned, refused, aborted etc. □

10. Depth of clinical expression • peripheral angiography • special peripheral angiography procedures • peripheral graft arteriogram • femoral-femoral crossover arteriogram □

11. How is it organised? • Multiple top level concepts, e.g: • body structure • Each with a hierarchy of concepts beneath • Strictly organised by ‘IS A’ relationships • index finger ‘is a kind of’finger • finger‘is a kind of’hand part,etc • Each concept may have permitted qualifiers, e.g. • pain ‘has qualifier’severity□

14. How is it constructed? • Defining and qualifying characteristics used to construct & refine a terminological model of healthcare • Concepts combined with Attribute-Value pairs • Procedure with: • method – excision • site – both tonsils • using – laser device (the post-coordinated representation) = Bilateral laser tonsillectomy (the pre-coordinated equivalent & a ‘kind of’ tonsillectomy) • ‘Method’, ‘site’ & ‘using’ are defining characteristicsAn additional ‘success’ attribute would be a qualifier □

15. Getting the right Snomed CT term • Search for term if you think it’s in there • Search the term hierarchies to find the term • Use a combination of the two • Info. can always be entered in post-coordinated form, q.v. the bilateral laser tonsillectomy example, but equivalent pre-coordinated term may be available • Where system constrains context, a data entry template can have possible terms in manageable drop-down lists (including post-coordination qualifiers) • Automatic encoding of entered text • highly desirable, but far from reliable at present • generated codes must be approved by user before commital □

16. Snomed-specific issues • Detecting equivalence of same thing said in pre-coordinated & various post-coordinated representations • Expressing negation - this comes in many forms, e.g: • diabetesexcluded • appendectomy not done • nopain in right leg • NAD- nothing abnormal detected • Consistent authoring of the terminology • Enabling accurate speedy use in unconstrained situations, e.g. when taking a patient history □

17. - & non-Snomed-CT specific issues • Human beings are lazy & good at inference • So patient records full of short cuts, e.g: • BP 140/80 means ‘blood pressure taken and systolic pressure observed to be 140 mm hg, and diastolic pressure 80 mm hg’. Assumed to be of patient whose record it’s in, & taken during the encounter it lies within • Computers are pedantic & pernickety. So is Snomed. It has xx codes for a blood pressure • Users want biggest bang per keystroke buck, so unconstrained searching for terms & post-coordination not popular □

18. Why is Snomed CT ‘not sufficient’? • Snomed CT consists of concepts, i.e. types • Doesn’t deal with numeric values, e.g. weight 70 kg • Doesn’t identify individual objects, e.g. people • So needs to be used within an external syntax to bind instances of Snomed concepts to their context, e.g.: • who it’s about - the subject (typically a patient) • when action / event occurred or observation made • who performed action / made observation • where action / event occurred or observation made □

19. Where are we now? • Snomed CT adopted by the NHS • Now in the hands of an independent international body • Adopted by several countries, more coming • Has no significant global rivals • But not much practical experience in patient record keeping with it yet, virtually none in real-time □

20. Are we winning? • “We will know we have succeeded when clinical terminologies in software are used and re-used,and when multiple independently developed medical records, decision support, and clinical information retrieval systems sharing the same information using the same terminology are in routine use.” • Alan Rector 2000 • “Clinical Terminology: Why is it so hard?”