The stability of VIII:C in frozen stored plasma samples--re-examined

VIII procoagulant activity (VIII:C) was estimated by a two-stage assay method, on 100 pre- and post-transfusion samples obtained from severe haemophiliacs receiving regular treatment with a variety of VIII concentrate preparations. Close and significant correlation (r = 0.97 P less than 0.01) was obtained between freshly tested samples and samples stored for one month at -35 degrees C. No significant difference between the two samples was demonstrated by Student's paired-t-test. Forty-nine of the stored samples were also measured for VIII procoagulant antigen (VIII:C Ag) level. A similar close and significant correlation was found for this parameter (r = 0.9 P less than 0.01), when compared with the VIII:C of the freshly tested samples. On average the VIII:C Ag value was 10% lower than the corresponding VIII:C value, although the difference was not statistically significant.