CLSI H47

One-Stage Prothrombin Time (PT) Test and Activated Partial Thromboplastin Time (APTT) Test, 3rd Edition

This document provides guidelines for performing the PT and APTT tests in the clinical laboratory, for reporting results, and for identifying sources of error.

This document is available in electronic format only.

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Chairholder: Donna Castellone, MS, MASCP, MT(ASCP)SH and Karen Moser, MD

Date of Publication: March 7, 2023

Order Code PDF: CLSI H47Ed3E
ISBN Number: 978-1-68440-173-4

Order Code Print: print not available

Edition: Third

Pages: 56

CLSI H47 Additional Details

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The U.S. Food and Drug Administration (FDA) has evaluated and recognized this approved-level consensus standard for use in satisfying a regulatory requirement.

CLSI H47 Abstract

Clinical and Laboratory Standards Institute document H47—One-Stage Prothrombin Time (PT) Test and Activated Partial Thromboplastin Time (APTT) Test describes the principles and procedures necessary for the routine performance of the PT and APTT by conventional techniques using citrated plasma. Each of the two tests measures the time for a fibrin clot to develop in test plasma after activation. The chemical reactions are complex and, characteristically, results are affected by preexamination (preanalytical) and examination (analytical) variables. The PT and APTT are important screening tests used in laboratory evaluation of patients suspected to have disorders of blood coagulation, including the presence of circulating coagulation inhibitors. The PT measures the extrinsic or tissue factor pathway of the coagulation system and is used to monitor vitamin K antagonist therapy. The APTT measures the intrinsic coagulation pathway and is used in monitoring heparin therapy, as well as parenteral direct thrombin inhibitor anticoagulant therapy such as argatroban and lepirudin. The objective of this guideline is to improve test reproducibility through standardization of technique and ensure clinical relevance by setting test performance goals. The document also highlights the international effort for standardization of the PT through the use of the international normalized ratio.