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Top LOINC Codes – Orders and Observations

Project information

LHNCBC, in cooperation with Regenstrief Institute, obtained and analyzed statistical data from many health care organizations to identify the most frequent subset that organizations could target for mapping. It obtained frequency distribution for three years of laboratory tests sources, including from Partners of Boston and the Indiana Network for Patient Care (an HIE), and United Healthcare, all of whom had mapped the test results to LOINC. The sample size of the combined sources was 490 million test results. We took tests within the top 99.8 percentile of test codes from each system, and included any test that reached that threshold, to obtain about 2000 common tests. Notably, 20% of the tests from each source were not included in the either of the other two. We created an analogous list of frequent test orders after analyzing LOINC frequency statistics from the same three large sources, and a few smaller sources with input from major referral laboratories about laboratory tests. Because so many orders are panels and the frequency distribution of order codes is even more skewed than tests codes, the top orders list was shallower.

LOINC Top 2000++ Lab Observations v1.6 :

This list is for laboratories, practices, researchers, and others who wish to map their laboratory test codes to universal LOINC codes ( The “Mapper’s Guide” provides a starter, target set of more than 2000 LOINC codes against which to map local test codes. The Top 2000+ list represents about 99.8% of the test volume carried by three large organizations in the United States that mapped all of their laboratory tests to the LOINC codes. Each row carries information about one laboratory test observation including its LOINC code and name, example units of measure expressed in UCUM units (, its relative frequency (rank), guidance (in some cases) about when to choose that test code, and more. To improve the accuracy of mapping, we also added short paragraphs of guidance based on literature research to highlight sets of codes that are prone to mis-mapping, e.g. D-Dimer has one test defined in units of DDU and other in DFU, and the amount of D-Dimer reported under one test is double that of the other. This document is the US version, which favors reporting in mass units, e.g. mg/dL, compared to the SI version which favors reporting in molar units, e.g. mmol/L.

You can obtain this guide in an Excel and CSV file format, as well as the SI versions on the LOINC website (

LOINC Universal Lab Orders Value Set v2.0

The Universal Lab Order Codes Value Set (a.k.a. Common Lab Orders) from LOINC is a collection of the most frequent lab orders. It was created for order entry system developers so that they could deliver them in HL7 messages to laboratories. On receipt, laboratories could understand and translate these universal codes into their internal processes for fulfillment.

This value set was developed iteratively through both empirical and consensus-driven approaches by the NLM, Regenstrief Institute, and several organizations. It contains an empirical list of the most commonly ordered tests, and was further expanded with the S&I Framework Initiative in 2014. The file contains the LOINC code, a unique numeric identifier with a check digit, the LOINC long common name for the term, and whether the term can be used as an Order, an Observation, or Both. Find more information here:

Downloads for LOINC Observations and Lab Orders Value Sets: