LOINC and Other Standards

How do I decide which coding systems to use?

Each coding system is designed for a specific purpose. The following is a brief discussion of a coding systems.


LOINC codes are useful for both ordering and resulting of test results. LOINC has been widely recognized and recommended for transmitting laboratory and clinical observations in HL7 messages. A short (non-exhaustive) list of recommendations include:

  • In 1999, LOINC was identified by the HL7 Standards Development Organization as a preferred code set for laboratory test names in transactions between health care facilities, laboratories, laboratory testing devices, and public health authorities.
  • The Consolidated Health Informatics initiative adopted LOINC to standardize the electronic exchange of clinical laboratory results and federally required patient assessment instruments with functioning and disability content.
  • The proposed rule for the HIPAA Administrative Simplification: Standards for Electronic Health Care Claims Attachments recommends standards that will facilitate the electronic exchange of clinical and administrative data to further improve the claims adjudication process when additional documentation (also known as health care claim attachments) is required. The rule proposes the adoption of the LOINC for specific identification of the additional information being requested, and the coded answers which respond to the requests.


CPT codes may be used for ordering and billing purposes. Often, CPT codes are not as specific as LOINC codes. For example, one CPT code may have multiple LOINC codes associated with it. Many lab tests will not have specified CPT codes associated with the "parts" of a lab test. For example, % basos, though there is a CPT code tor order a differential (Blood count; automated differential WBC count), but there is not an individual code to represent the result of percent basophils in a differential.

The National Library of Medicine has sponsored a LOINC to CPT mapping. The first draft mappings are available through the UMLS website and NLM is happy to receive comments about the usefulness of this mapping.


SNOMED is a large, comprehensive computerized clinical terminology covering clinical data for diseases, clinical findings, and procedures. In HL7 ORU messages, LOINC provides codes for the question (OBR-4, OBX-3) while SNOMED provides codes for the answers (OBX-5).

Is there a LOINC to CPT mapping available?

Yes and no. The National Library of Medicine sponsored a LOINC to CPT mapping that was performed by Intermountain Health Care and reviewed by Regenstrief and the AMA in 2005-06. That effort mapped terms from LOINC version 2.15 to the 2005 version of CPT and covered many, but not all, of the common laboratory tests. The original intent was to periodically update and expand the LOINC to CPT mappings, but due to funding and other resource issues, the project did not continue.

The basic use-case for the original mapping effort was that LOINC codes would be used for ordering/reporting tests and observations, and the associated CPT codes would be used for billing; thus, this was a unidirectional map from LOINC codes for orders/results to CPT billing codes. The mapping table and more information about the process and mapping assumptions that were made are available through NLM's UMLS website.

How are LOINC codes different from ICD codes?

The International Classification of Diseases (ICD) is primarily a code system for recording diagnoses whereas LOINC is a code system for identifying test observations. There are a few test codes in ICD-10 Clinical Modification (ICD-10-CM) for use in hospital billing only.

Knowledge Base

Users’ Guide

Search Syntax