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New ICSH Guidance published for measurement of factor VIII and factor IX type I inhibitors

July 2023

ICSH, the International Council for Standardization in Haematology is pleased to announce the Publication of a new ICSH Guideline for laboratory measurement of factor VIII and factor IX type I inhibitors.

Author Contributions

Piet Meijer: Drafting manuscript.

Flora Peyvandi, Guy Young, Rajiv Pruthi, Simara de Lima Montalvao and Steve Kitchen critically reviewed, edited and approved the final manuscript.


Prepared on behalf of the International Council for Standardisation in Haematology, the aim of the document is to provide guidance and recommendations on the measurement of factor VIII (FVIII) and factorIX (FIX) inhibitors.

After an introduction on the clinical background and relevance of factor VIII and factor IX inhibitor testing, the following aspects of laboratory testing are included: screening for inhibitors, assay principle, sample requirements, testing requirements and interpretation, quality assurance, interferences and recent developments.

This guidance document focusses on recommendations for a standardised procedure for the laboratory measurement of FVIII and FIX type I inhibitors.

The recommendations are based on published data in peer-reviewed literature and expert opinion.


First published: 07 June 2023

By the International Journal of Laboratory Hematology Volume 45, Issue 4 Aug 2023 Pages i-iv, 405-619

The publication is available to:



The International Council for Standardization in Haematology (ICSH) was initiated as a standardization committee by the European Society of Haematology (ESH) in 1963 and officially constituted by the International Society of Hematology (ISH) and the ESH in Stockholm in 1964.

​The ICSH is a not-for-profit non-governmental organisation that aims to achieve reliable and reproducible results in laboratory analysis in the field of diagnostic haematology.

​The ICSH coordinates Working Groups of experts to examine laboratory methods and instruments for haematological analyses, to deliberate on issues of standardization and to stimulate and coordinate scientific work as necessary towards the development of international standardization materials and guidelines.

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