Structure of Domain Coverage

SNOMED CT includes 19 domains arranged in a polyhierarchical structure. Each hierarchy is an ordered organization of concepts linked together through IS A relationships. Each concept may have one or more parents.

The hierarchical arrangement is helpful for locating concepts, grouping similar concepts, and conveying meaning. For example, if we see the concept cell under the concept anatomic entity we will understand the intended meaning as different than if it appeared under the concepts room or power source(Desiderata for Controlled Medical Vocabularies in the Twenty-First Century by J.J. Cimino published in Methods of Information in Medicine 1998:37:394-403).

Concepts are linked to their more general parent concept codes directly above them in a hierarchy. Concepts with more general meanings are usually presented as being at the top of the hierarchy and then at each level down the hierarchy, the meanings become increasingly more specific or specialized.

The domains contain all of the components (clinical, administrative, database structure, as well as other components that express how the domains relate to each other) necessary to create SNOMED CT concepts and maintain the database structure.

Definition	Notes	Examples
A domain is a set of concepts that the Concept Model permits to be defined or refined, using a particular set of attributes and ranges. Some domains do not have attributes and ranges, but may if a concept model is created	A domain, to which an attribute can be applied, is typically defined to include concepts in one or more branches of the subtype hierarchy	The domain of 116676008 | Associated morphology (attribute)| is defined as subtype of 404684003 | Clinical finding (finding)| The range of values of 116676008 | Associated morphology (attribute)| is subtypes of 49755003 | Morphologically abnormal structure (morphologic abnormality)|

The following table lists the domains, definitions, and examples. *Those without a concept model are marked with an asterisk.

Domains/Top-level hierarchies

Body structure	Anatomical or acquired body structure Morphologic abnormality (subtype of body structure)	181492002 |Entire skin of back (body structure)| 52988006 |Lesion (morphologic abnormality)|
Clinical finding	Clinical finding: normal/abnormal observations, judgments, or assessments of patients Disorder: always and necessarily an abnormal clinical state	39579001 |Anaphylaxis (disorder)| 167222005 |Abnormal urinalysis (finding)|
Environment and Geographical location	Environment: types of environments Geographical Location: named locations such as countries, states, or regions	405607001 |Ambulatory surgery center (environment)| 223528007 |Somalia (geographic location)|
Event	Occurrences impacting health or health care; not procedures or interventions	417928002 |Abuse (event)| 2641000119104 |Exposure to chlamydia (event)|
Observable entity	Information about a quality/property to be observed and how it will be observed	423493009 |Age at diagnosis (observable entity)| 416125006 |Concentration of hemoglobin in erythrocyte (observable entity)|
Organism	Organisms of significance to human and animal medicine; use in modeling cause of disease	3265006 |Genus Candida (organism)| 710877000 |Beta lactam resistant bacteria (organism)|
Pharmaceutical/Biological Product	Drug products (not Substances)	116768003 |Autologous packed red cells product (product)| 317222006 |Product containing precisely cimetidine 200 milligram/1 each conventional release oral tablet (clinical drug)|
Physical force*	Forces applied to the body that may cause injury	57955009 |Hot weather (physical force)| 285719001 |Mechanical abrasion (physical force)|
Physical object*	Physical devices relevant to health care, or to injuries/accidents	15237007 |Sitz bath chair, device (physical object)| 42974001 |Club, device (physical object)|
Procedure	Procedure: activities performed in the provision of health care (includes medical history-taking, physical examination, diagnostic and therapeutic interventions, training and education, and counseling) Regime/therapy (subtype of procedure): set of procedures focused on a single purpose on one patient over time (e.g. repeated administration of drug in a small dose for an indefinite period of time)	54321008 |Cardiac flow imaging (procedure)| 386513007 |Anesthesia management (procedure)|
Qualifier value*	One of several possible values for an attribute used to define concepts	90734009 |Chronic (qualifier value)| 263714004 |Colors (qualifier value)|
Record artifact*	Clinical documents, or parts thereof	229059009 |Report (record artifact)| 41000179103 |Immunization record (record artifact)|
Situation with explicit context	Concepts that include context information; a subtype of the situation to which it applies with an attribute associating it with the relevant clinical finding or procedure May be used to represent conditions/procedures that already occurred, haven't yet occurred, or refer to someone else (not patients)	169594005 |Late onset antenatal care (situation)| 413174003 |Statin not tolerated (situation)|
SNOMED CT Model Component*	Concepts and attributes necessary to organize and structure SNOMED CT terminology and its derivatives	900000000000442005 |Core metadata concept (core metadata concept)| 370136006 |Namespace concept (namespace concept)|
Social context*	Social conditions and circumstances related to healthcare Subtypes include: ethnic group, life style, occupation, person, racial group, religion/philosophy, s ocial concept	58626002 |Legal guardian (person)| 413323004 |Refugee family (social concept)|
Special concept*	Navigational concept (to support locating concepts in hierarchies)	363743006 |Navigational concept (navigational concept)|
Specimen	Entities that are obtained (usually from patients) for examination or analysis	373193000 |Lymph node from sentinel lymph node dissection (specimen)| 258441009 |Exudate specimen (specimen)|
Staging and scales*	Assessment and tumor staging scales	273472005 |Functional status index (assessment scale)| 1287643004 |International Neuroblastoma Risk Group staging system (tumor staging)|
Substance	Active chemical constituents of allergens, agents, substances, chemicals, drugs, and materials (not Pharmaceutical/Biological Products)	89889006 |Cotton fiber (substance)| 64856004 |Digestive system fluid (substance)|

Granularity

The scale, or level of detail, in a terminology is called granularity. Concepts and meanings range from very general, or coarse, to very specific, or fine. SNOMED CT has multiple granularities, which is an important component of terminologies that are multipurpose. The broader meanings are useful for aggregation (e.g. Clinical finding, Procedure, etc.), but are not intended for recording individual patient data.

The progressive levels of refinement are used to meet clinical data requirements. There are, however, limits to the degree of precoordination of certain types of complex statements.

In general, concepts in SNOMED CT should name things that exist in the real world. The concepts are usually names or short noun phrases, not complete sentences or paragraphs.

SNOMED CT is intended to be used with electronic health applications that can support full clinical statements, along with their attributions, dates, times, and statement interrelationships. It may be challenging to balance SNOMED CT content with the needs of those using electronic health applications. For example, some older applications may require concepts outside of the scope of SNOMED CT. SNOMED CT tries to maximize its usefulness and at the same time minimize precoordination.

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