OMOP Domains

This document provides an overview of the OMOP Common Data Model (CDM) domains, which are used to classify and standardize diverse clinical concepts across observational healthcare data. Each domain serves a specific role in representing information about patients, encounters, and clinical activities, ensuring semantic clarity and interoperability within the OHDSI framework.

Domain	Definition	CDM Table(s)
Condition	Represents concepts indicating clinical states observed, diagnosed, or reported for a patient, including diseases, disorders, signs, and symptoms. Conditions describe an assertion about health status, not a performed action or a measured result. Typically derived from problem lists, diagnosis billing codes, or clinical documentation.	CONDITION_OCCURRENCE, CONDITION_ERA
Drug	Covers terms representing chemical or biological substances formulated to exert a therapeutic effect when introduced into the body. Encompasses drug products, active ingredients, delivery forms (e.g., oral tablets, injections, topical creams), vaccines, and combination products. Unlike Devices, which act through physical means, Drugs primarily act through chemical or biological mechanisms.	DRUG_EXPOSURE, DRUG_ERA
Device	Represents physical objects, instruments, or materials used in patient care for diagnostic, therapeutic, preventive, or assistive purposes, acting by mechanical, structural, or material means rather than chemical action. This domain includes implantable devices such as pacemakers, stents, and artificial joints; external devices such as wheelchairs, braces, and oxygen masks; instruments used in medical procedures such as defibrillators and catheters; clinical materials such as adhesives, surgical supplies, and dental materials; monitoring equipment such as infusion pumps and ventilators; prosthetics and assistive technologies; contrast agents, nutritional products, food supplements, infant formula, as well as blood products and blood derivatives including packed red blood cells, platelets, plasma, and cryoprecipitate. Devices differ from Drugs, which exert their intended effect through chemical or biological action, and from Procedures, which represent the clinical use or placement of a device rather than the device itself.	DEVICE_EXPOSURE
Procedure	Defines activities or interventions (actions) ordered by or performed by healthcare providers for diagnostic, therapeutic, or preventive purposes. Examples include surgeries, imaging studies, biopsies, and catheterizations. Compared to Measurements, Procedures record the act of performing an activity (e.g., 4307315 “Gram stain microscopy” [performed, with no result recorded]), while Measurements capture the result or findings from that activity (e.g., “Gram stain microscopy” [with result, such as detection of Gram-positive cocci]). Compared to Devices, Procedures involve clinical activities, whereas Devices represent tangible instruments used. For example, “Oxygen administration by non-rebreather mask” is a Procedure, while “Non-rebreather oxygen mask” is a Device.	PROCEDURE_OCCURRENCE
Measurement	Represents terms related to structured, standardized evaluations or tests performed on a person or their specimen, yielding numeric, categorical, or ordinal results. Includes laboratory tests/procedures, vital signs, pathology reports with quantitative findings, assessment instruments such as staging, scales, and scores (but not all of them), observable entities with information about a quality or property to be observed (but not all of them), some clinical findings with qualitative results of testing. Measurements differ from Procedures in that they capture the measured result, not the act of measurement itself. Measurements differ from Observations in that they are structured, objective outputs of standardized assessments, often with units or standardized categories.	MEASUREMENT
Observation	Encompasses clinical facts, findings, or statements about a patient that are not covered by other domains. Includes medical and family history, social determinants of health, patient-reported outcomes, lifestyle factors (e.g., smoking status), or subjective assessments (e.g., patient feels well). Observations are often qualitative, subjective, or context-driven and may or may not arise from a formal test. They differ from Conditions, which represent defined diseases or pathological states requiring diagnosis, and from Measurements, which represent standardized numeric or categorical results obtained through structured testing.	OBSERVATION
Specimen	Represents concepts describing biological samples collected from a person for laboratory testing, clinical diagnostics, biobanking, or research purposes. Specimen concepts standardize the nature of the sample (e.g., “Blood specimen”, “Tumor tissue specimen”, “Saliva sample”) and are used to classify biological material consistently within the OMOP Vocabulary.	SPECIMEN
Visit	Defines the context of healthcare encounters, grouping clinical activities by encounter type. Includes outpatient visits, emergency department encounters, inpatient stays, and more granular units (ICU or observation room). Visits provide a temporal and contextual framework for interpreting other events (Conditions, Procedures, Measurements).	VISIT_OCCURRENCE, VISIT_DETAIL
Provider	Represents concepts describing individual human healthcare professionals involved in the delivery of patient care. This includes physicians, nurses, pharmacists, therapists, and other clinical practitioners. Provider concepts capture the role or type of healthcare professional, distinct from Care Site concepts, which represent institutions, facilities, or organizational locations where care is provided.	PROVIDER