ACCURACY OF ANTI-FACTOR XA-ACTIVITY DETERMINATION OF UNFRACTIONATED AND LOW-MOLECULAR HEPARIN - A COLLABORATIVE STUDY IN THE FEDERAL-REPUBLIC-OF-GERMANY AND THE FORMER GERMAN-DEMOCRATIC-REPUBLIC

A collaborative study was performed with the aim of defining the accuracy of anti-factor Xa-activity determination of unfractionated (UF) and low molecular weight (LMW) heparin. An unfractionated heparin was assayed against the 4th international standard for UF-heparin, and a LMW-heparin against the 1st international standard of LMW-heparin using the chromogenic S-2222 substrate assay. Plasma samples containing three different concentrations of the two heparins were assayed by 13 laboratories in the Federal Republic of Germany and the former German Democratic Republic. Three of the 13 laboratories obtained anti-factor Xa-activities which were 40% too low. The coefficient of variation of 10/13 laboratories ranged from 10% to 23% for UF and LMW heparin at the three concentrations. These data demonstrate that the values of anti-factor Xa-activity measured with the chromogenic substrate assay tend to be too low. The coefficients of variation are low for an interlaboratory control study, so that the determination of the anti-factor Xa-activity is a useful method for clinical and scientific purposes. The measurement of anti-factor Xa-activity is simple, valid and useful for collaborative studies.