low adamts13 activity fig1 these results show that anti adamts13 autoantibodies were present in the acquired ttp plasma but not in the normal plasma and that autoantibodies in plasma from a patient with acquired ttp can be detected using this method other fluorescent adamts13 substrates can be substituted for lvy amc this method can be used to distinguish between congenital ttp and acquired ttp fig1 shows that the level of inhibition of adamts13 activity on platelets is dependent on the amount of anti adamts13 autoantibodies used in the assay and thus the anti adamts13 activity plasma from an acquired ttp patient was diluted to different amounts 10 20 and 40 in normal plasma and incubated with isolated platelets in a total volume of 90 u03bcl for 15 minutes ten u03bcl of 8 mm lvy amc substrate was added and the fluorescence was determined after incubation at 37 u00b0 c for 1 hour the inhibition of adamts13 activity by ttp plasma was dependent upon the amount of ttp plasma used in the assay the amount of fluorescence generated over time in the assay is dependent upon the amount of platelets used in the assay as shown in fig2 a higher fluorescent signal was generated in the control normal plasma without anti adamts13 antibodies using more platelets the addition of acquired ttp plasma containing adamts13 antibodies almost completely inhibited adamts13 activity regardless of the amount of platelets in.