A model for a multicentre approach to the derivation of reference intervals for thyroid hormones and testosterone for laboratories using identical analysers

Ideally, every laboratory should derive their own reference intervals for a ll analytes, but this is difficult in practice. A survey, by questionnaire, of UK laboratories using the Chiron Diagnostics ACS:180 (Chiron Diagnostic s Limited, Halstead. Essex, UK), for thyroid function tests, showed that 10 % of laboratories derived their own reference intervals, 60% quoted values "adapted" from intervals for previous methods, whilst the remaining 40% quo ted (often incorrectly) reference intervals supplied by the manufacturer. I n addition only 13% of respondent laboratories derived their own reference intervals for testosterone. As a result of this survey, a study was devised to enable the users of the Chiron Diagnostics ACS:180 immunoassay system t o develop and use within-method, between-laboratory reference intervals for thyroid hormones and testosterone. Laboratory collaboration provided the r ecommended minimum number of data points by establishing a reference sample group. This sample group was used for the calculation of appropriate refer ence intervals for each hormone according to the guidelines published by th e IFCC. We propose this approach as a model for laboratories using identica l instrumentation to produce, through collaboration, within-method, between laboratory reference intervals.