Clinical and Laboratory Standards Institute document H02-A5-Procedures for the Erythrocyte Sedimentation Rate Test; Approved Standard-Fifth Edition is a revision of the fourth edition approved standard (H02-A4) published in December 2000. The document outlines the necessary details for the performance of a standardized (Westergren) method on diluted (1:4) blood specimens for the determination of the erythrocyte sedimentation rate (ESR). Quality assurance and evaluation of other methods to measure the ESR are also described, including procedures for the preparation of a fresh blood reference material for use in the laboratory or manufacturing of ESR devices. This standard provides guidance for the validation, verification, quality assurance, and quality control of ESR measurement devices or related controls. The intended audience includes manufacturers of such devices, end-user clinical laboratories, accrediting organizations, and regulatory bodies.