Comparison of methods of plasma volume determination for dose calculation of factor VIII in patients with classic haemophilia
Ockelford, P.A.; Lowe, G.; Johns, A.S.; Berry, E.W.
New Zealand Medical Journal 99(796): 116-119
1986
ISSN/ISBN: 0028-8446 PMID: 3081842 Document Number: 272458
Plasma volumes have been measured in 12 patients with moderate or severe haemophilia A and compared with plasma volumes derived by calculation using a variety of commonly recommended formulae based on body weight with or without a correction for haematocrit. The mean plasma volume by measurement was 47 ml/kg. A calculated plasma volume using 42 ml/kg and a correction for haematocrit most closely approximated the measured results. The correlation coefficient was 0.9. Ex vivo factor VIII recoveries, following infusion of either lyophilised cryoprecipitate or NZFVIII (controlled pore glass preparation), were then determined based on the observed/expected response assuming different values for plasma volume. Mean recoveries of approximately 100% were associated with a 2.4% FVIII rise per unit/kg administered using cryoprecipitate. Ex vivo recoveries following NZFVIII exceeded 100% with mean values, depending on the technique used for plasma volume determination, up to 131%. Recoveries were not significantly affected by the plasma volume method used and all methods indicated that the labelled potency of NZFVIII is currently being underestimated by at least 20-30%.