Clin Biochem Rev 2008; 29 Supplement(i):S23-S26

Evaluating Assay Precision

Douglas Chesher
Department of Clinical Biochemistry, Pacific Laboratory Medicine Services, Royal North Shore Hospital,
St Leonards NSW 2065, Australia.
For correspondence: Dr Douglas Chesher e-mail: dougc@med.usyd.edu.au

Summary
• When evaluating the precision of a method it is necessary to assess the repeatability (within-run) and the total or withinlaboratory
precision.
• It is insufficient to assess repeatability in a single run.
• Clinical and Laboratory Standards Institute (CLSI) document EP05-A2 describes the protocols for determining the precision
of a method.1 The precision of a method should be tested at at-least two levels; each run in duplicate, with two runs per day
over 20 days.
CLSI document EP15-A2 describes the protocols that should be undertaken by the user to verify precision claims by a
manufacturer. Precision claims by a manufacturer should be tested at at-least two levels, by running three replicates over five
days.2
• A spreadsheet for assisting with the calculations described in this article is available from the AACB web-site.3.