Abstract

P1580 An improved simpler method for using the ReFactotm Laboratory Standard in monitoring patients receiving BDDrFVIII NIA Exhibition Area 09:30 17th July, 2003 Session Type: Posters Subject area: Methods Session title: Methods in coagulation Abstract: P1580 Authors: C. Hillman-Wisman*, L. Llanto*, W. Hollon* & J. M. Lusher* *Children's Hospital of Michigan, USA B-Domain deleted (BDD)rFVIII (Wyeth's ReFactotm) was licensed for use in the U. S. in March, 2000. BDDrFVIII has been shown to be essentially identical to plasmaderived FVIII with respect to functional properties, vWF binding kinetics, and pharmacokinetics. However, in patients (pts) infused with it, one-stage APTT based FVIII assays give lower than expected values (on ave., 50% less), while two stage and chromogenic assays give expected (calculated) values. This assay discrepancy has been shown (by Mikaelsson et al.) to reflect a difference in phospholipid binding with BDDrFVIII. Since almost all coagulation laboratories (labs) employ the onestage FVIII assay for clinical use, Wyeth has attempted to deal with the assay discrepancy by providing a ReFactotm Laboratory Standard (RLS) to be used instead of a plasma standard when performing FVIII assays on recipients of BDDrFVIII ('like vs. like' concept). However, use of the RLS lab reference calibrator as directed is time consuming (approx. 1 h) making it less likely to be used by clinical labs. We have considerably shortened lab preparation time by preparing larger volumes of the RLS working standard (WS) diluted with FVIII deficient plasma to yield 1.0 U/mL, snap freezing diluted aliquots in polystyrene capped tubes, and storing them at -80 °C. To use, an aliquot is thawed quickly in 37 °C water bath (2 min). We determined the stability of the frozen RLS standard aliquots over a 7 mos. period, with interassay variability being less with the frozen RLS-WS (C.V. 6.5% vs. 7.5% for freshly prepared RLS-WS). Cumulative data showed much less variability over time with the frozen standard (7.7% vs. 10.8% for fresh). We also found greater consistency in assaying 3 SSC standards (S1, S2, S3) using the frozen RLS-WS (half the variability of the fresh RLS-WS). Additionally, the same plasma samples from pts. receiving BDDrFVIII were assayed by one-stage FVIII method using the frozen RLS-WS and by chromogenic assay; there was excellent correlation between these results. Thus, the snap-frozen aliquots of RLS-WS are stable at -80 °C for at least 7 mos., their use gives more reliable results, is more time efficient for the lab (2 min vs. 1 h.), and there is less chance for error. file:////ddn-453/d/ML3G-Data/JTH-Abstract-2003/HTML/Thursday/Abstract%20P1580.html (1 of 2) [1/27/2014 4:29:50 PM]