Being philosophical for a moment, every known object that has a significant importance attributed to it has a name. The organs you are using to read these words are known as eyes. The words are written on pieces of paper called pages. To turn the pages, you use your hands. These are all objects that we have named so that we can identify them easily.

In healthcare, important entities—diseases, procedures, lab tests, drugs, symptoms, bacteria species, for example, have names and identities too. For example, the failure of the heart valves to pump blood to the rest of the body is known as heart failure. ACE inhibitors are a class of drugs used to treat heart failure.

A problem arises, however, when healthcare industry workers associate the same entity with different identities. For example, one physician may refer to "heart failure" as "congestive heart failure", while another may refer to it as "CHF." Also, there are varying levels of specificity: a third doctor may call it "systolic heart failure" to indicate that the dysfunction is occurring during the systolic phase of the heartbeat. In medicine, accuracy and specificity are of the utmost importance. How can we ensure that all members of the healthcare team are talking and thinking about the same thing? The answer lies in clinical codes.

Clinical codes can be thought of as unique identities for medical concepts. Each code is typically comprised of a pair of objects: an alphanumeric code and a verbal description of the entity that the code represents. For example, in the ICD10-CM coding system, the code I50.9 represents "Heart failure, unspecified." There are additional, more specific codes to represent more specific heart failure diagnoses when they are known.

There are likely thousands of different coding systems that exist in the world, many of them being used only in the specific healthcare organization at which they were conceived. Fortunately, to ease confusion and promote interoperability, there are several well-known coding systems that are seen as national/international standards. Some of the more important standardized coding systems include International Classification of Disease (ICD) for medical diagnoses, Current Procedural Terminology (CPT) for medical procedures, Logical Observation Identifiers Names and Codes (LOINC) for laboratory tests, National Drug Code (NDC) for drug therapies, and Systematized Nomenclature of Medicine (SNOMED) for all of the preceding and more. In this section, we explore each of these coding systems in a little more detail.