In Vivo Recovery of Fviii:c in Hemophilic Patients

Abstract

Average pre‐operative in vivo recoveries of factor VIII:C concentrate fell from 1967 to 1976, then improved, and fell again in the early 1980's. Average outpatient in vivo recoveries were studied from 1978‐83; the lowest values for two of three brands were seen in 1980. Standard in vivo recovery studies were performed with a 10 minute post‐infusion plasma sample only, but detailed tests in 39 patients indicated that the peak post‐infusion level after concentrate infusion occurred at 30 minutes rather than 10 minutes in 23 percent of recipients. Comparison of one‐ and two‐stage assay methods showed that higher in vivo recoveries were obtained when plasma samples were assayed with the two‐stage method. The major cause of discrepancies between observed and expected VIII:C recoveries, however, is believed to be inaccurate assessment of the VIII:C potency of various in‐house VIII:C references. Methods of in vitro assay of concentrates which adequately predict in vivo effect are needed.