In vivo recovery of FVIII:C in hemophilic patients.

:  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.