SNOMED CT contains more than 357,000 health care concepts with unique meanings and formal logic-based definitions organized into hierarchies. A unique semantic type, included in parentheses, identifies each hierarchy in the fully specified name of every concept in the hierarchy. The fully populated code system list with unique descriptions for each concept contains more than 957,000 descriptions. Approximately 1.37 million semantic relationships exist to improve the reliability and consistency of data retrieval.

SNOMED CT is a general clinical reference terminology, meaning its intent is to represent clinical concepts across many domains, which includes conditions, diagnoses, symptoms, and signs, all of which are a type of finding. SNOMED CT also represents procedures, observations, and some laboratory tests, drugs, and devices. The table also notes concepts used for ancillary aspects for documentation of the domains. As a general reference terminology, the expectation is for SNOMED CT to provide many of the concepts needed for clinical information encoding, and unless otherwise noted, a specific terminology should be the primary source for standardized terminology encoding.

There is no intent for SNOMED CT codes to transmit all possible information about a condition, observation, or procedure. The intent is for SNOMED CT codes to identify the condition, observation, or procedure.

Measure developers should use the CVX code set for coding vaccine-allergy-inducing entities.

Measure developers should use the SNOMED CT substance hierarchy for coding non-medication allergy-inducing entities.

SNOMED CT-Specific Guidance for Measure Developers for Allergy Value Sets

Use SNOMED CT to represent allergen drug class concepts only when following this guidance. Refer to the RxNorm section and the Electronic Clinical Quality Improvement (eCQI) Resource Center for additional guidance.

In addition to the required approach for representing medication allergen (or ingredient) substances using RxNorm ingredient type concepts noted, electronic clinical quality measures (eCQMs) can add SNOMED CT drug class concepts to represent medication allergens. If deemed appropriate by the measure developer for use in the measure, the expectation is for the drug class concept to include SNOMED CT drug class concepts only when the measure developer anticipates a general drug class concept in patient records as an indication the patient is allergic to all drugs in the class.

Measure developers should

• Keep in mind that when using a drug class concept, this means that no drug in the class can be an expected therapy for the patient.
• Review all defined drugs for inclusion in the class when choosing to include the SNOMED CT drug class concept.
• Also define an RxNorm Allergy value set with the specific ingredient (IN) and precise ingredient (PIN) term types (TTY) drug ingredients that represent the drug class.

Grouping Value Sets

While not required, measure developers may create a grouping value set that groups both the RxNorm ingredient type allergy value set and the SNOMED CT drug class allergy value set into one grouping value set referenced in the measure. A grouping value set is a list of several value sets that share a common purpose and similar concepts. For CMS eCQMs, specifically, members of a grouping value set must have the same QDM Category, but the value set members of the grouping do not need to share the same code system. Using a grouping value set eases development and testing burden on electronic health record vendors. See also the eCQI Resource Center for more value set information.

SNOMED CT Maintenance

SNOMED International owns and maintains the SNOMED CT technical design, core content architecture, SNOMED CT Core content, and SNOMED CT documentation. SNOMED CT content includes the technical specification of SNOMED CT and fully integrated multi-specialty clinical content. The core content includes the concepts table, description table, relationships table, history table, ICD-10-CM mapping, and Technical Implementation Guide. Each SNOMED CT code for a concept is unique and permanent.

SNOMED CT Distribution

In the United States, the National Library of Medicine (NLM) distributes SNOMED CT, which acts as the U.S. SNOMED CT Release Center. There are multiple SNOMED CT Release Centers across the globe and many, including the NLM, release a specific edition of SNOMED CT for use in their specific realm. The U.S. Edition of SNOMED CT contains the combination of the International Core (same in every edition of SNOMED CT) and a U.S.-specific extension that contains concepts only in use within the U.S. Thus, the U.S. Edition of SNOMED CT contains some SNOMED CT concepts that do not appear in other editions, such as those used in Canada or in the United Kingdom. Over time, promotion of realm-specific concepts may occur from the realm-specific edition to the International Core and then these concepts are available to all users. When this occurs, the concept identifier will not change. Only the U.S. Edition of SNOMED CT is available for use in the U.S.

Request New SNOMED CT Concepts

At times, a measure developer may need to request a new SNOMED CT concept. The measure developer should submit the request through the US SNOMED CT Content Request Service (USCRS). The requester will need an IHTSDO account to access the USCRS. The U.S. team evaluates the request and determines whether to include a useful addition only in the U.S. Edition of SNOMED CT or also to promote to the International Core. Measure developers should account for contractual timelines when considering applying for new concepts. For information on obtaining the standard, contact SNOMED International or the NLM.