Introduction to LOINC

LOINC (Logical Observation Identifiers Names and Codes) provides a set of universal names and ID codes for identifying laboratory and clinical test results.

LOINC currently provides ~92,000 entries that define the names and IDs of laboratory tests. The following shows three examples of LOINC codes:

Each LOINC entry represents a laboratory test.

Parts of LOINC entry

• LOINC: unique identifier

• Name: structured term name

• Component: defines the analyte in the test

• Property: defines “kinds of quantities”. It can be divided into five several categories, mass, substance, catalytic activity, and number or counts. Each category is further divided into subclasses, for example MCnc or “mass concentration” is a subclass of “mass” property, while NCnc or “number of concentration (count/vol)” and Naric or “number aeric (number per area)” are subclasses of counts.

• Time: defines whether a measurement was made at a moment, or aggregated from a series of physiologic states. The three examples are all PT (“points”), meaning that they are measurements at a single time point. As an example, a test on “daily urine amount” will be labeled as 24H (“24 hours”).

• Aspect: defines a modifier for a measurement over a duration. For example, “8H^max heart rate” means the “max” heart rate measured during an 8-hour period. Min, max, first, last, mean typically appear here.

• System: can be considered as the specimen for the test, such as “serum”, “blood”, “urine”, “cerebrospinal fluid” etc.

• Scale” defines the scale of the measurement. Scale is the most important information for our application. The following table summarizes possible values of scale.

• Method: defines the method used for the measurement.

Table 1: LOINC Scale Types

Scale Type	Abbr.	Description
Quantitative	Qn	The result of the test is a numeric value that relates to a continuous numeric scale.
Ordinal	Ord	Ordered categorical responses, e.g., positive, negative;
Quantitative	OrdQn	Test can be reported as either Ord or Qn.
Nominal	Nom	Nominal or categorical responses that do not have a natural ordering.
Narrative	Nar	Text narrative.
“Multi”	Multi	Many separate results structured as one text “glob”
Document	Doc	A document that could be in many formats (XML, narrative, etc.)
Set	Set	Used for clinical attachments

Qn, Ord and Nom are the three most frequently used LOINC codes, accounting for about 99% of data. Qn typically makes up about 80% of cases.