Body weight and fat mass index as strong predictors of factor VIII in vivo recovery in adults with hemophilia A.

BACKGROUND: The treatment of hemophilia A requires infusions of factor VIII (FVIII) concentrates. The number of units to be given in order to obtain the target level is calculated using the formula: [body weight (BW) × desired FVIII increase]/2, which assumes that each unit infused per kg of BW increases the FVIII level by 2%.
OBJECTIVES: The present observational study evaluated the dependence of FVIII recovery on different morphometrical variables: BW, fat mass index (FMI), body mass index, and the difference between actual and ideal BW. PATIENTS AND METHODS: FVIII recovery was measured in 46 non-actively bleeding hemophilia A patients, being treated with a recombinant FVIII concentrate. Regression trees were used to identify morphometrical predictors of recovery.
RESULTS: The median recovery was 2.08 for all patients, 2.63 for those with a BW ≥ 81.0 kg and 1.87 for others (P < 0.001). The recovery was significantly higher when FMI was ≥ 20% compared with FMI < 15% (median recovery: 2.35 vs. 1.74; P = 0.007). Using regression trees, three groups were created: BW < 80.5 kg and FMI < 22.3%, BW < 80.5 kg and FMI ≥ 22.3% and BW ≥ 80.5 kg. Median recovery in these groups was 1.80, 2.16 and 2.63, respectively (P < 0.001).
CONCLUSIONS: The dose calculation of FVIII should take into account both BW and FMI, and be adapted to underweight or overweight patients. Comparison of the average recovery after different FVIII concentrates should keep in mind morphometrical patient characteristics.