Principles of in vivo Recovery and Survival Studies

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Abstract
Factor VIII preparations available to the clinician are numerous and vary greatly in their mode of preparation, potency, purity and potential side effects. In vivo behaviour of Factor VIII:C from each product should be studied systematically. Collection of useful and valid information on VIII:C recovery and half‐life requires the observance of rather strict rules. Standards. The dose of infused VIII:C can be calculated either from the labeled value or from local measurement using as reference a concentrate calibrated against the WHO concentrate standard. VIII:C plasma levels are tested using a plasma reference calibrated against the WHO plasma standard. Patients. Severe hemophilia A patients non bleeding or bleeding in small capacity joint and not treated for at least five days without inhibitor are selected. Dose. At least 20 u/kg body weight of VIII:C are infused. Sampling. Plasma samples collected before, 15, 30 and 60 minutes post‐infusion allow to identify the peak of VIII:C activity from which in vivo recovery is calculated. Samples collected 4,8–12,24 and 36–48 h post‐infusion allow to evaluate F VIII:C half‐life on the basis of VIII:C plasma levels measured in 4 of these samples. Assays. VIII:C one or two‐stage assays are equally acceptable although only one‐stage assays detect activated VIII:C. Plasma samples from a patient are stored at ‐70°C and all tested in one session. Calculations. In vivo recovery is estimated as percent of a theoretical value obtained either on the basis of 1 u/kg VIII:C provides 0.02 u VIII:C/ml plasma or of a calculated plasma volume. Various calculation programs seem suitable for evaluation of VIII:C half‐life.

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