Get started with LOINC

Your organization wants to exchange health data—like labs, vitals signs, and clinical documents—but different systems have different ways of identifying the same test or measurement. Fragmentation has created islands of isolation.

The solution is to map your local test codes to a universal standard that every system can understand. This is where LOINC comes in. LOINC is the go-to terminology for identifying tests and observations.

LOINC is one of many standards used to identify health data. LOINC codes represent the “question” for a test or measurement. Sometimes the “answer” is a numeric value and units. Qualitative results are often coded using SNOMED CT. A diagnosis may be represented with ICD. In the U.S., a procedure is often identified by CPT®.

HL7® is the carrier of this encoded, digital data, either via its HL7® Version 2 (the older standard) or HL7® FHIR® (the powerful newcomer). Using either standard, LOINC is the primary, preferred code system for clinical and laboratory observations.

A LOINC code is a number followed by a dash and a single number known as a check digit. The code itself has no intrinsic meaning, though they are created sequentially. There are currently 109,325 codes in the LOINC database.

A numeric LOINC code is a permanent and unique identifier. The code combined with its corresponding text name is known as a “term”. The term represents an individual clinical concept with all appropriate granularity.

LOINC’s goal is to create different codes for each test, measurement, or observation that has a clinically different meaning. LOINC codes distinguish a given observation across six dimensions (or axes) that we call Parts. These Parts are like the LEGO® bricks that come together to create a LOINC.

Also like LEGO bricks, LOINC Parts are reusable. Each Part has its own code that looks like a normal LOINC code, except prefixed with “LP”. These atomic pieces enable many things including the translation of LOINC into other languages.

Component

Sometimes called Analyte, this is the entity being measured or observed.

Property

This is the characteristic or attribute of the component being observed.

Timing

Or simply Time, it is the interval of time over which an observation was made.

System

The thing upon which the observation was made. Also referred to as Specimen.

Scale

How the observation value is quantified or expressed: quantitative, ordinal, nominal.

Component
Leukocytes
Also known as white blood cells

LP14419-3

Property
NCnc
LOINC’s abbreviation for Number Concentration

LP6836-3

Timing
Pt
LOINC’s abbreviation for Point in Time

LP6960-1

System
CSF
The standard abbreviation for Cerebral Spinal Fluid

LP7156-5

Scale
Qn
LOINC’s abbreviation for Quantitative

LP7753-9

Text-based labels or names are associated with LOINC codes for human readability. As mentioned previously, the Fully-Specified Name (FSN) for a LOINC is the concatenation of its six main Parts separated by colons. Each LOINC can have multiple names populated. By its nature, a FSN is always defined. So too is its Long Common Name (LCN). Other labels include Short Name, Display Name, and Consumer Name.

Which name you use in your systems depends on use case. The FSN works best in mapping scenarios when examination of meaning is critical. A LOINC’s LCN is the recommended choice in most other contexts.

Generally speaking, the scope of LOINC is anything you can test, measure, or observe about a patient. There are two major divisions of the content in LOINC:

• Laboratory
• Clinical

We refer to these divisions in the LOINC database as Class Types. (We do carve out surveys into a separate Class Type though they can be considered “clinical.”)

The laboratory (or simply “lab”) portion of LOINC covers anything that you can test, measure, or observe about a specimen—that is, a sample removed from a patient. This contains the categories of chemistry, hematology, serology, microbiology (including parasitology and virology), toxicology; as well as categories for cell counts, antibiotic susceptibilities, and more.

In addition to class types of lab and clinical, we create LOINC codes in two basic forms:

• Discrete observations
• Collections of observations

There are LOINC codes for individual observations and measurements, including:

• Single lab tests (e.g., glucose [mg/dL] in urine)
• Questions on a survey or form (e.g., “are you able to jump up and down?”)
• Measurements on a patient (e.g., body height)
• Distinct elements on a report (e.g., physical observations about gait)

For much of its history, LOINC was only available as a download. It still is, but we have added other means to get LOINC codes. In addition to a downloadable file, you can also access the terminology via several APIs, including the standard FHIR® API created by HL7®. We have an entire web page dedicated to all the ways you can access LOINC.

Since its inception, Regenstrief has developed LOINC as an open standard. We welcome requests for new concepts. It is because of submissions from the LOINC community that we’ve been able to grow and adapt so quickly. We are also always happy to receive specific suggestions about revisions or enhancements to existing content like synonyms and term descriptions as well.

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