Fig. 4. Plasma-supplemented kaolin activated clotting time (ACT) values versus  ex vivo  r-hirudin concentrations in two patients. The linear relationship is represented with the following linear equation: hirudin concentration = PM-ACT * 0.067–8.5, r²=0.74. The solid horizontal line represents predicted regression line from the ex vivo  analysis (two patients) whereas the dotted horizontal line represents the predicted line from the in vitro  analysis. Vertical arrows depict 95% confidence intervals at three concentrations (e.g. , 0, 2, 4 μg/ml) of hirudin as obtained from the previously published in vitro  analysis. 12Although the slope and intercept have changed when ex-vivo  hirudin concentrations are compared with the calculated in vitro  concentrations, nearly all PM-ACT data points fall within these confidence intervals.