Standardization of Low Molecular Weight Heparins : A Collaborative Study

Abstract

SummaryA 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.

Low-Molecular-Weight Heparin Fraxiparin® in Chronic Hemodialysis

“…However, a com parison of the AXa activities that we ob served with those reported by other authors is not presently possible since there is no common standard for LMWH. This is why our AXa activity curve was calibrated against Fraxiparin rather than against UFH as several authors did [18][19][20], AH that clearly shows that it is not necessary to ad just Fraxiparin doses or to monitor blood Fraxiparin levels by means of AXa activity measurements.…”

Heparin and low-molecular-weight heparin

“…However, when the first samples of LMWH were assayed against the UFH Standard this was clearly not the case -there was large variability between laboratories, even when ostensibly using the same method. For instance, the coefficient of variation (CV) among seven laboratories carrying out a chromogenic method on the same LMWH sample was 43% (47). There was also a tendency to non-parallelism between the log dose -response lines of the LMWH and UFH Standard, rendering many of the assays statistically invalid.…”

Problems In Laboratory Monitoring Of Heparin Dosage

“…There is evidence that the spread of results in different centres assaying samples from patients receiving three different LMWH preparations could be reduced if LMWH was used in the construction of calibration lines in place of standard heparin and there is evidence that the WHO International Standard for unfractionated heparin is unsuitable as a standard for LMWH assays (Barrowcliffe et al, 1985). The standard of choice for calibration of anti-Xa assays for monitoring LMWH therapy should therefore be a LMWH that has been calibrated against the 1st WHO International Standard for LMWH (Barrowcliffe et al, 1988).…”