Summary
A collaborative study was carried out, in which eight laboratories each assayed eight
low molecular weight (LMW) heparins against the International Standard (IS) for heparin.
APTT assays and three types of anti-Xa method were used. The results of this study
showed that:
1. LMW heparins cannot be validly assayed against the IS by APTT or anti-Xa methods.
2. Potencies of LMW heparins vs. the IS differed considerably between the four types
of assay method used and also between different laboratories using the same type of
method.
3. Adoption of a single LMW heparin standard would improve validity, improve inter-laboratory
variation, and largely abolish the differences between the three types of anti-Xa
method. However, since calibration of a LMW heparin standard against the IS would
give potencies that differ widely by the different assay methods, a single assay method
such as the anti-Xa amidolytic, plasma, would need to be chosen for this calibration.
Keywords
LMW heparin - Assay - Standards
