Clinical and Laboratory Standards Institute guideline H48—Determination of Coagulation Factor Activities Using the One-Stage Clotting Assay provides information to be used in harmonizing laboratory testing of factor assays. It provides laboratories with guidelines to optimize factor assay testing by minimizing the effect of variation in preexamination, examination, and postexamination processes. It identifies good laboratory practices related to analyzer and reagent performance, reference intervals, lot-to-lot validation, quality assurance, and quality control issues. Standardizing assay performance provides patients with the best outcomes with regard to both diagnosis and treatment. This guideline is written for laboratorians and/or diagnostic testing personnel responsible for factor assay testing, physicians (eg, hematologists, pathologists) responsible for interpreting results, external quality assessment programs, and manufacturers of factor assay testing reagents and test systems.

This guideline replaces the previous edition of the approved guideline, H48-A, published in 1997. Several changes were made in this edition including: 

• Expanded terminology 

• Use of factor assays to aid in diagnosis of coagulation disorders 

• Enhanced preexamination, examination, and postexamination activities and sources of error 

• Identification and reporting of inhibitors 

• Anticoagulation effect on factor assays 

• Reagents and reagent responsiveness 

• Lot-to-lot verification

This guideline provides specifications for the one-stage clotting factor assay. It is intended to increase the diagnostic usefulness of the one-stage factor assay by providing the laboratory with necessary tools to minimize the effects of variables and to provide guidelines to enhance the precision and accuracy of patient results. Preexamination, examination, and postexamination issues specific to factor activity testing are covered. 

This guideline is written for laboratory and/or diagnostic testing personnel responsible for factor assay testing including the performance, QC, and reporting of assays of coagulation factor activity, physicians (eg, hematologists, pathologists) responsible for interpreting results, external quality assessment (EQA) programs, and manufacturers of factor assay testing reagents and test systems. 

This guideline does not cover chromogenic, two-stage clotting, antigenic, or manual methodologies for factor assays. Assays for fibrinogen, von Willebrand Factor (VWF), Factor XIII (FXIII), or contact factors of high molecular weight kininogen or prekallikrein are not covered in this guideline. Assays used to quantify inhibitors to specific factors are not covered in this guideline.