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The top of the SNOMED CT hierarchy is occupied by the root concept (|SNOMED CT concept|). All concepts are descended from this root concept through at least one sequence of |is a| relationships. This means that the root concept is a supertype of all other concepts and all other concepts are subtypes of the root concept.
The direct subtypes of the root concept are referred to as 'Top Level Concepts'. These concepts are used to name the main branches of the hierarchy. Each of these Top Level Concepts, together with their many subtype descendants, forms a major branch of the SNOMED CT hierarchy and contains similar types of concepts. As the hierarchies descend (that is, more |is a| relationships are added below the Top Level Concepts) the concepts within them become increasingly specific.
Below is a list of the Top Level Concepts with a brief description of the content represented in their branch of the hierarchy.

• |Clinical finding| represents the result of a clinical observation, assessment or judgment and includes normal and abnormal clinical states (e.g. |asthma|, |headache|, |normal breath sounds|). The |clinical finding| hierarchy includes concept used to represent diagnoses.
• |Procedure| represents activities performed in the provision of health care. This includes not only invasive procedures but also administration of medicines, imaging, education, therapies and administrative procedures (e.g. |appendectomy|, |physiotherapy|, |subcutaneous injection|).
• |Situation with explicit context| represents concepts in which the clinical context is specified as part of the definition of the concept itself. These include presence or absence of a condition, whether a clinical finding is current, in the past or relates to someone other than the subject of the record (e.g. |endoscopy arranged|, |past history of myocardial infarction|, |family history of glaucoma|).
• |Observable entity| represents a question or assessment which can produce an answer or result (e.g. | systolic blood pressure|, |color of iris|, |gender|).
• |Body structure| represents normal and abnormal anatomical structures (e.g. |mitral valve structure|, |adenosarcoma|).
• |Organism| represents organisms of significance in human and animal medicine (e.g. |streptococcus pyogenes|, |beagle|, |texon cattle breed|).
• |Substance| represents general substances, the chemical constituents of pharmaceutical/biological products, body substances, dietary substances and diagnostic substances (e.g. |methane|, |insulin|, |albumin|).
• |Pharmaceutical/biologic product| represents drug products (e.g. |amoxicillin 250mg capsule|, |paracetamol + codeine tablet|).
• |Specimen| represents entities that are obtained (usually from the patient) for examination or analysis (e.g. |urine specimen|, |prostate needle biopsy specimen|).
• |Special concept| represents concepts that do not play a part in the formal logic of the concept model of the terminology, but which may be useful for specific use cases (e.g. |navigational concept|, |alternative medicine poisoning|).
• |Physical object| represents natural and man-made physical objects (e.g. |vena cava filter|, |implant device|, |automobile|).
• |Physical force| represents physical forces that can play a role as mechanisms of injury (e.g. |friction|, |radiation|, |alternating current|).
• |Event| represents occurrences excluding procedures and interventions (e.g. |flood|, |earthquake|).
• |Environments and geographical locations| represents types of environments as well as named locations such as countries, states and regions (e.g. |intensive care unit|, |academic medical center|, |Denmark|).
• |Social context| represents social conditions and circumstances significant to health care (e.g. |occupation|, |spiritual or religious belief|).
• |Staging and scales| represents assessment scales and tumor staging systems (e.g. |Glasgow Coma Scale|, |FIGO staging system of gynecological malignancy|).
• |Qualifier value| represents the values for some SNOMED CT attributes, where those values are not subtypes of other top level concepts. (e.g. |left|, |abnormal result|, |severe|).
• |Record artefact| represents content created for the purpose of providing other people with information about record events or states of affairs. (e.g. |patient held record|, |record entry|, |family history section|).
• |SNOMED CT Model Component| contains technical metadata supporting the SNOMED CT release.

Concept Model Attributes – Representing Characteristics of a Concept

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