American Society of Hematology

Figure 2.

$Ticagrelor inhibits platelet activation by HIT antibodies in functional assays. (A) Five different known HIT+ sera were spiked with increasing concentrations of ticagrelor and assessed using the HIPA test in the presence of 0.2 aFXaU/mL reviparin, with dimethyl sulfoxide as a carrier control. The lag time until platelet aggregation is shown on the y-axis (reversed). A lag time < 35 minutes (dotted line) corresponds to a positive HIPA test. The ticagrelor concentration used is shown on the x-axis, with the observed therapeutic range in patients depicted as a shaded area. Four of 5 tested sera became negative when ticagrelor was present in this range. Error bars represent the range of lag time observed in 4 donor test cells. (B) Total IgG was isolated from the index patient’s serum and tested using the HIPA test, which resulted in fast and strong activation of donor platelets (within 5 minutes). When the IgG fraction was respiked with ticagrelor, the HIPA test was again inhibited. The elution buffer served as a negative control. Data are shown as the mean and standard deviation (SD) of lag time observed with washed platelets from 3 donors. (C) Two sera (ie, the index patient and a serum known to contain platelet-activating antibodies and prespiked with ticagrelor) were tested in the HIPA test in the presence or absence of the ticagrelor antidote PB2452. In the absence of PB2452, both sera gave false-negative results, which were fully reversed by PB2452. Inhibition by high-dose heparin confirmed the specificity of the reaction and ruled out an unspecific effect of PB2452; PB2452 does not activate platelets in the case of HIT− serum. Data are shown as mean and SD of lag time of the 2 tested sera with washed platelets of 3 donors. (D) Sera of 3 known HIT patients were tested in the HIPA test. For all 3 HIT cases, the sera were positive in the presence of heparin and became negative after being spiked with ticagrelor. When the ticagrelor-spiked serum was also incubated with activated charcoal (AC), the HIPA test was positive again. No unspecific activation of platelets by AC was observed (HIT− serum incubated with AC). Data are shown as mean and SD of lag time of the tested sera with ≥3 donors. AC, 20 mg of active charcoal powder; Tica, ticagrelor; UFH, high-dose heparin (100 IU/mL).$

Ticagrelor inhibits platelet activation by HIT antibodies in functional assays. (A) Five different known HIT⁺ sera were spiked with increasing concentrations of ticagrelor and assessed using the HIPA test in the presence of 0.2 aFXaU/mL reviparin, with dimethyl sulfoxide as a carrier control. The lag time until platelet aggregation is shown on the y-axis (reversed). A lag time < 35 minutes (dotted line) corresponds to a positive HIPA test. The ticagrelor concentration used is shown on the x-axis, with the observed therapeutic range in patients depicted as a shaded area. Four of 5 tested sera became negative when ticagrelor was present in this range. Error bars represent the range of lag time observed in 4 donor test cells. (B) Total IgG was isolated from the index patient’s serum and tested using the HIPA test, which resulted in fast and strong activation of donor platelets (within 5 minutes). When the IgG fraction was respiked with ticagrelor, the HIPA test was again inhibited. The elution buffer served as a negative control. Data are shown as the mean and standard deviation (SD) of lag time observed with washed platelets from 3 donors. (C) Two sera (ie, the index patient and a serum known to contain platelet-activating antibodies and prespiked with ticagrelor) were tested in the HIPA test in the presence or absence of the ticagrelor antidote PB2452. In the absence of PB2452, both sera gave false-negative results, which were fully reversed by PB2452. Inhibition by high-dose heparin confirmed the specificity of the reaction and ruled out an unspecific effect of PB2452; PB2452 does not activate platelets in the case of HIT⁻ serum. Data are shown as mean and SD of lag time of the 2 tested sera with washed platelets of 3 donors. (D) Sera of 3 known HIT patients were tested in the HIPA test. For all 3 HIT cases, the sera were positive in the presence of heparin and became negative after being spiked with ticagrelor. When the ticagrelor-spiked serum was also incubated with activated charcoal (AC), the HIPA test was positive again. No unspecific activation of platelets by AC was observed (HIT⁻ serum incubated with AC). Data are shown as mean and SD of lag time of the tested sera with ≥3 donors. AC, 20 mg of active charcoal powder; Tica, ticagrelor; UFH, high-dose heparin (100 IU/mL).

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