> ## Documentation Index > Fetch the complete documentation index at: https://docs.metriport.com/llms.txt > Use this file to discover all available pages before exploring further. # Overview > Learn about medical coding systems and how we apply them. Medical coding systems are common vocabularies that allow specific identification of different clinical concepts. There are a number of common and widely used medical coding systems, such as ICD-10-CM, SNOMED, and others. However, different healthcare IT systems use all kinds of coding systems - some standardized, some proprietary. Metriport enriches data with code system lookup, normalization, and cross-walks, so that the result is cohesive and more robust than it is at the source. ## Common Medical Coding Systems You can use the URLs of these systems from the table below to filter for relevant codes in your patient's [Consolidated Bundle](/medical-api/api-reference/fhir/consolidated-data-query-post). Below is an overview of the most prevalent coding systems supported by Metriport and often found in the source documents: | Coding System | Identifiers | Purpose | FHIR Resources | Example | Maintained by | | :- | :- | :- | :- | :- | :- | | [ICD-10-CM](https://www.cdc.gov/nchs/icd/icd-10-cm/index.html)
(International Classification of Diseases, 10th Revision, Clinical Modification) | OID: 2.16.840.1.113883.6.90
URL: [http://hl7.org/fhir/sid/icd-10-cm](http://hl7.org/fhir/sid/icd-10-cm) | Encodes medical diagnoses and conditions | Condition | `E11.9` → *Type 2 diabetes mellitus without complications* | U.S. National Center for Health Statistics (NCHS) | | [CPT](https://www.ama-assn.org/topics/cpt-codes)
(Current Procedural Terminology) | OID: 2.16.840.1.113883.6.12
URL: [http://www.ama-assn.org/go/cpt](http://www.ama-assn.org/go/cpt) | Encodes outpatient medical procedures and services | Procedure | `0331T` → *Myocardial sympathetic innervation imaging, planar qualitative and quantitative assessment* | American Medical Association (AMA) | | [CVX](https://www2a.cdc.gov/vaccines/iis/iisstandards/vaccines.asp?rpt=cvx)
(Vaccine Codes) | OID: 2.16.840.1.113883.12.292
URL: [http://hl7.org/fhir/sid/cvx](http://hl7.org/fhir/sid/cvx) | Identifies vaccines and vaccine groups | Immunization | `125` → *Novel Influenza-H1N1-09, live virus for nasal administration* | U.S. Centers for Disease Control and Prevention (CDC) | | [SNOMED CT](https://www.snomed.org/what-is-snomed-ct)
(Systematized Nomenclature of Medicine – Clinical Terms) | OID: 2.16.840.1.113883.6.96
URL: [http://snomed.info/sct](http://snomed.info/sct) | Encodes comprehensive clinical terminology for conditions, findings, and procedures | Condition, Procedure, and others | `44054006` → *Diabetes mellitus type 2 (disorder)* | SNOMED International | | [LOINC](https://loinc.org/)
(Logical Observation Identifiers Names and Codes) | OID: 2.16.840.1.113883.6.1
URL: [http://loinc.org](http://loinc.org) | Encodes laboratory and clinical observations | Observation, Encounter, and others | `718-7` → *Hemoglobin \[Mass/volume] in Blood* | Regenstrief Institute | | [NDC](https://www.fda.gov/drugs/drug-approvals-and-databases/national-drug-code-directory)
(National Drug Code) | OID: 2.16.840.1.113883.6.69
URL: [http://hl7.org/fhir/sid/ndc](http://hl7.org/fhir/sid/ndc) | Identifies drug products marketed in the U.S. | Medication | `0002-8215-01` → *insulin human (Humulin R) 100 \[iU]/mL Parenteral Injection, Solution, 1 VIAL, MULTI-DOSE in 1 CARTON (0002-8215-01) / 10 mL in 1 VIAL, MULTI-DOSE* | U.S. Food and Drug Administration (FDA) | | [RxNorm](https://www.nlm.nih.gov/research/umls/rxnorm/index.html) | OID: 2.16.840.1.113883.6.88
URL: [http://www.nlm.nih.gov/research/umls/rxnorm](http://www.nlm.nih.gov/research/umls/rxnorm) | Normalizes drug names and clinical drugs | Medication | `311036` → *HumuLIN R 100 UNT/ML Injectable Solution* | U.S. National Library of Medicine (NLM) | ## Other Clinical Classification Systems These systems are typically not provided in the source documents, but are added by Metriport: | Coding System | Purpose | FHIR Resources | Example | Maintained by | | :- | :- | :- | :- | :- | | [CCSR](/medical-api/fhir/coding-systems/ccsr)
(Clinical Classifications Software Refined) | Groups ICD-10-CM diagnosis codes into clinically meaningful categories across body systems | Condition | `END002` → *Diabetes mellitus without complication* | U.S. Agency for Healthcare Research and Quality (AHRQ) | | [HCC](https://www.cms.gov/medicare/payment/medicare-advantage-rates-statistics/risk-adjustment)
(Hierarchical Condition Categories) | Groups ICD-10-CM diagnosis codes into hierarchical categories used for risk adjustment and reimbursement | Condition | `18` → *Diabetes with chronic complications* | U.S. Centers for Medicare & Medicaid Services (CMS) | | [CCIR](https://www.hcup-us.ahrq.gov/toolssoftware/ccsr/chronic.jsp)
(Chronic Condition Indicator Refined) | Classifies ICD-10-CM diagnosis codes as chronic or nonchronic across 18 clinical condition categories | Condition | `C` → *Chronic* | U.S. Agency for Healthcare Research and Quality (AHRQ) | ## Representation in FHIR Each of these coding systems appears in FHIR as elements of `coding`, `category`, or `extension` arrays. Here's a subset of attributes you can expect to find in a Condition resource, displaying how Metriport uses different coding systems to hydrate the clinical data: ```json theme={null} { "resourceType": "Condition", "code": { "text": "Unspecified atrial fibrillation", "coding": [ { "code": "I48.91", "display": "Unspecified atrial fibrillation", "system": "http://hl7.org/fhir/sid/icd-10-cm" }, { "code": "49436004", "system": "http://snomed.info/sct", "display": "Atrial fibrillation (disorder)" }, { "code": "427.31", "display": "Atrial fibrillation, unspecified type (HCC)", "system": "http://terminology.hl7.org/CodeSystem/ICD-9CM-diagnosiscodes" } ] }, "category": [ { "coding": [ { "system": "http://terminology.hl7.org/CodeSystem/condition-category", "code": "encounter-diagnosis", "display": "Encounter Diagnosis" } ], "text": "Encounter Diagnosis" }, { "coding": [ { "system": "https://hcup-us.ahrq.gov/toolssoftware/ccsr/ccs_refined.jsp", "code": "CIR", "display": "Diseases of the circulatory system" } ], "text": "Diseases of the circulatory system" } ], "extension": [ { "url": "http://hl7.org/fhir/StructureDefinition/condition-related", "valueCoding": { "code": "C", "display": "Chronic", "system": "https://public.metriport.com/fhir/StructureDefinition/condition-chronicity.json" } }, { "url": "https://public.metriport.com/fhir/StructureDefinition/condition-hcc.json", "valueCodeableConcept": { "coding": [ { "system": "http://terminology.hl7.org/CodeSystem/cmshcc", "display": "Unspecified atrial fibrillation", "version": "v24", "code": "96" } ] } } ] } ``` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.