Category User guide Organisation Logical Observation Identifiers Names and Codes (LOINC) Type Standard Version 2020 Access Open Status Active Updated Jun-25 This document is part of Section 12 G of the Users' Guide for LOINC. LOINC is an international standard for identifying health measurements, observations and documents such as laboratory and clinical test results.Section 12 of the Users' Guide provides information to help users of LOINC make the best use of the standard. Section 12 G contains 11 technical briefs that have been developed for various LOINC terms to clarify either the meaning, current nomenclature or use case of a given term. This brief is about free thyroxine index variants. Access Users' Guide: 12 G - LOINC Technical Briefs: Free Thyroxine Index Variants v2020 By accessing this content, you are leaving this website. The Agency takes no responsibility for the accuracy of content on the destination page.