ABSTRACT
The use of international biological standards during the last 30 years has proved
extremely successful in promoting global harmonization of estimates between laboratories
and methods. Experience has led to the identification of physical criteria essential
for standards to be suitable for long-term use. High precision of liquid filling coupled
with low residual moisture and oxygen and the use of sealed glass ampoules have been
found consistent with homogeneous and stable International Standards (ISs). Most plasma
coagulation factors and inhibitors are calibrated in International Units (IU), which
are defined as the amount of analyte in 1 mL of normal pooled plasma. Adoption of
the IU has provided clarity in the definition of normal and abnormal states and has
facilitated dose calculation for replacement therapy. The assay of like-versus-like
materials (e.g., concentrate versus concentrate) has been found to improve interlaboratory
agreement and there are now both plasma and concentrate ISs available for many coagulation
factors and inhibitors. Studies into the assay of recombinant factor VIII have indicated
that additional measures, such as modifications to assay methodology, are necessary
to reduce interlaboratory variability. This experience may prove valuable in the future,
when we have to deal increasingly with the challenges to standardization associated
with the products of bioengineering.
KEYWORDS
International Standard - coagulation factors - factor VIII - hemophilia
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Dr. Anthony R Hubbard
Haemostasis Section, Biotherapeutics Group, National Institute for Biological Standards
and Control, Blanche Lane, South Mimms
Potters Bar, Hertfordshire, EN6 3QG, United Kingdom
Email: thubbard@nibsc.ac.uk
