Ian Herbert

Vice Chair

BCS Health Informatics Forum

With grateful acknowledgements to Dr David Gain of NHS CFH

SNOMED Clinical Terms (Snomed CT) SNOMED Clinical Terms (Snomed CT)

– the language for healthcare– the language for healthcare

A presentation for the KIDDM Mashup, A presentation for the KIDDM Mashup, 1717thth September 2007 September 2007

Why do we need Snomed-CT?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 □

What is SNOMED CT?What is SNOMED CT?

Dictionary of Clinical Concepts

Thesaurus of Terms

Thesaurus of TermsHealth

Lexicon

A controlled clinical vocabulary

A controlled clinical vocabulary

A conceptual classification

SNOMED CT is a terminological resource that can be implemented in software applications to represent clinically relevant information reliably and reproducibly □

Why not use ICD10 or OPCS4?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 □

What’s wrong with free text?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 □

How is the information How is the information usedused??

Direct care

Indirect Care

Decision support

Clinical audit Summaries

Reporting

Documentation in electronic records

Epidemiology

ResearchResource

management

Aggregation functionality

Billing & reimbursement

Administrative / management

information

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

One concept, many namesOne concept, many names

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 □

Avoiding ambiguityAvoiding ambiguity

Will the computer limit what I Will the computer limit what I cancan say? 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. □

Depth of clinical expressionDepth of clinical expression

peripheral angiography

special peripheral angiography procedures

peripheral graft arteriogram

femoral-femoral crossover arteriogram □

How is it organised?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 □

Hierarchies Examples

Clinical Finding: Contains the sub-hierarchies of Finding and Disease    Important for documenting clinical disorders and examination findings

Finding: Swelling of arm Disease: Pneumonia

Procedure/intervention: Concepts that represent the purposeful activities performed in the provision of health care

Biopsy of lung Diagnostic endoscopy Foetal manipulation

Observable entity Concepts represent a question or procedure which, when combined with a result, constitute a finding

Gender Tumour size Ability to balance

Body structure Concepts include both normal and abnormal anatomical structures Abnormal structures are represented in a sub-hierarchy as morphologic abnormalities

Lingual thyroid ( body structure) Neoplasm (morphologic abnormality)

Hierarchies Examples

Organism Coverage includes animals, fungi, bacteria and plants Necessary for public health reporting and used in evidence-based infectious disease protocols

Hepatitis C virus Streptococcus pyogenes Acer rubrum (Red maple) Felis silvestris (Cat)

Substance Covers a wide range of biological and chemical substances Includes foods, nutrients, allergens and materials Used to record the active chemical constituents of all drug products

Dust Oestrogen Haemoglobin antibody Methane Codeine phosphate

Physical object Concepts include natural and man-made objects Focus on concepts required for medical injuries

Prosthesis Artificial organs Vena cava filter Colostomy bag

Physical force Includes motion, friction, electricity, sound, radiation, thermal forces and air pressure Other categories are directed at mechanisms of injury

Fire Gravity Pressure change

How is it constructed?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 characteristics An additional ‘success’ attribute would be a qualifier □

• 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 □

Getting the right Snomed CT termGetting the right Snomed CT term

Snomed-specific issuesSnomed-specific issues

• Detecting equivalence of same thing said in pre-coordinated & various post-coordinated representations

• Expressing negation - this comes in many forms, e.g:• diabetes excluded• appendectomy not done• no pain 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 □

- & non-Snomed-CT specific issues- & 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 □

Why is Snomed CT ‘not sufficient’?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 □

Where are we now?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 □

Are we winning?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?”