SNOMED Documentation Search
This section contains a high-level overview of SNOMED CT with some additional information
in areas of direct relevance to subsequent chapters of this guide. For a more complete
introduction to SNOMED CT see the SNOMED CT Starter Guide () and for more detailed information refer to the SNOMED CT Document Library (http://snomed.org/doc).
SNOMED CT is a clinical terminology with global scope covering a wide range of clinical
specialties, disciplines and requirements. As a result of its broad scope, one of
the benefits of SNOMED CT is a reduction of specialty boundary effects that arise
from use of different terminologies or coding systems by different clinicians or departments.
This allows wider sharing and reuse of structured clinical information. Another benefit
of SNOMED CT is that the same data can be processed and presented in ways that serve
different purposes.
SNOMED CT allows a range of different options for immediate retrieval and subsequent
reuse to address immediate and longer-term clinical requirements and the requirements
of other users. The nature of SNOMED CT hierarchies allows information to be selectively
retrieved and reused to meet different requirements at various levels of generalization
(e.g. retrieval of subtypes of |lung disorder| or |bacterial infection| would both include |bacterial pneumonia|).
SNOMED CT has a broad scope of coverage. It includes concepts representing the wide range of types of information that need to be recorded in clinical records. As a result, practitioners from different disciplines and specialties can use SNOMED CT to record appropriate data at different stages in the delivery of patient care.
SNOMED CT components consist of concepts, terms and relationships that enable effective
representation of clinical information.
Concepts: Every concept represents a unique clinical meaning, which is referenced using a unique,
numeric and machine-readable SNOMED CT identifier. The identifier provides an unambiguous
unique reference to each concept and does not have any ascribed human interpretable
meaning.
Descriptions: A set of textual descriptions are assigned to every concept. These provide the human
readable form of a concept.
Relationships: A relationship represents an association between two concepts. Relationships are
used to logically define the meaning of a concept in a way that can be processed by
a computer.
These components are supported by reference sets (refsets). Refsets are resources that can be used to customize and configure the
terminology for use in a particular country, organization, specialty or data entry
situation.
SNOMED CT concepts are related to one another within a subtype hierarchy. At the top of this hierarchy are general concepts referred to as top-level concepts. Most of the clinically relevant concepts in SNOMED CT fall under one of the following top-level concepts:
SNOMED CT concepts are also related to one another by defining relationships which
represent characteristics of the meaning of a concept. Each of these relationships
represents the value of an attribute. SNOMED CT currently uses more than fifty defining
attributes, each of which is identified by a concept.
The set of rules that defines the types of relationships permitted between concepts
is referred to as the concept model. These rules specify the set of concepts to which
an attribute can be applied (the 'domain' of the attribute) and the permitted set
of values for each attribute (the 'range' of the attribute).
From the perspective of the overlaps between SNOMED CT and LOINC the most significant
parts of the concept model are the subtypes of:
However in addition to this, concept s from several other SNOMED CT concept model domains provide non-numeric values that can be applied to a range of tests represented by LOINC Terms.
SNOMED CT relationships are validated and normalized using description logic (DL). The use of DL ensures logical consistency in the formal computer processable definitions of SNOMED CT concepts. This includes generation of a subtype hierarchy that is consistent with all the defining relationships. As a result, SNOMED CT is able to support more complete and consistent meaning-based retrieval than a terminology, classification or code system that is not validated using a formal logic.
SNOMED CT can represent clinical information by using concept identifiers as simple
codes in a patient record or message. However, it is also possible to express more
detailed information by combining concepts into a postcoordinated SNOMED CT expression.
SNOMED CT support of the postcoordination technique allows additional clinical detail
to be represented if required. For example, |pneumococcal pneumonia| has a |finding site| of |lung structure|, which can be refined to |right upper lobe of lung|.
Postcoordination greatly increases the depth of detail that SNOMED CT can represent
without having to include every possible specific site for every possible disorder
via a concept. For example, the concept |bacterial pneumonia| has a defining relationship specifying its |causative agent| as |bacteria| and this can be refined to |Streptococcus pneumoniae|.
SNOMED CT expressions are a structured combination of one or more concept identifiers
used to represent a clinical idea in a logical manner, which is automatically processable.
Expressions are represented using the SNOMED CT compositional grammar, which is a
lightweight syntax for the representation of SNOMED CT expressions.
Description logic allows alternative representations of the same or similar information
to be recognized and compared. For example, |pneumococcal pneumonia| refined by |finding site||right upper lobe of lung| can be computed to have the same meaning as |right upper lobe pneumonia| refined by |causative agent||Streptococcus pneumoniae|.
SNOMED CT is widely recognizes as the leading global healthcare terminology. In more
than 25 IHTSDO Member countries SNOMED CT can be used under a free license. SNOMED
CT is also used in more than forty non Member countries with low cost licenses for
usage. The up to date list of Members is shown at .
Within the USA, SNOMED CT has been adopted for use in problem list and quality measures
as part of the Centers for Medicare and Medicaid Services Electronic Health Record
(EHR) "Meaningful Use" incentive program as specified in the Standards and Certification
Criteria. SNOMED CT is also a core element in national EHR initiative in many other
IHTSDO Member countries and is widely used in healthcare communication standards including
HL7 and IHE.
SNOMED CT is maintained by IHTSDO, a not-for-profit association that is owned and
governed by its national Members. More than twenty-five countries are Members of IHTSDO,
and more join every year.
The International Edition of SNOMED CT is licensed by IHTSDO and updates are distributed
every six months. The tab delimited release files include versioning data that allows
changes to be tracked and supports generation of views of any earlier release.
SNOMED CT is designed to support national extensions that enable addition of local
translations and/or dialect variants, without undermining the global representation
of meaning using SNOMED CT concept identifiers. Extensions also allow addition of
national or local content specific to a particular region or use case.
Customizations represented using the SNOMED CT reference set mechanism allow sharable
configuration to address local, specialty or organizational requirements.