C.2 Calculating the check digit for LOINC Parts, Answers, and other identifiers with letters (KB)

C.2 Calculating the check digit for LOINC Parts, Answers, and other identifiers with letters

KB LOINC Users’ Guide Appendix C Calculating Mod 10 check digits C.2 Calculating the check digit for LOINC Parts, Answers, and other identifiers with letters

Calculating a check digit for a code containing a letter difference is different. This document details its algorithm.

Last updated on August 4, 2026 at 2:42 pm EDT

We use a variant of the basic Mod 10 algorithm to calculate LOINC Part, Answer List, Answer, and Group identifiers because those identifiers contain the alpha prefixes “LP”, “LL”, “LA”, and “LG”, respectively.

A detailed description of the method is documented the OpenMRS Wiki. This source also has code for calculating the check digit in numerous languages including Java, Python, JavaScript, and C#.

This same algorithm can be used for calculating check digits for user-assigned “X codes” (that contain a leading “X” character) as well.