The WFH/ICTH Study of the Sensitivity of Different Partial Thromboplastin Time Tests in Mild Haemophilia

The second phase of the WFH/ICTH study has been conducted by distributing some 40 snap-frozen coded plasma samples from normal subjects and mild haemophiliacs to seven U. K. laboratories, where they were tested with the Manchester PTT reagent (Dr. L. Poller) and seven commercial reagents. Each laboratory also assayed each sample (under different code) for VIIIc by the local method. Each laboratory used the Manchester reagent and a given pair of the commercial reagents throughout the study, so that each commercial reagent was used by two different laboratories. The correlation between VIIIc and PTT was imperfect, with consistant discrepancies across reagents for given samples, making clear that the PTT was affected by other plasma characteristics (presumably within the normal range) besides the low VIIIc. The ability of reagents to discriminate between ca 30 iu/dl and 100 iu/dl VIIIc appeared to be correlated with the slope of PTT on VIIIc in the range 5-30 iu/dl. The results from mild haemophiliacs and normal subjects will be reported in detail for each PTT reagent.