RBCs from patients with PV adhere in greater numbers to HUVECs than RBCs from healthy volunteers under static conditions. RBC adhesion was measured using ⁵¹Cr-labeled RBCs. The nonadherent RBCs were removed by successive washes,⁶  and the radioactivity was measured in each wash and in the remaining RBCs attached to the HUVECs. The number of adherent RBCs was calculated. The unbroken line within the box represents the median; the dotted line represents the mean. The vertical lines extending beyond the boxes indicate the 25% and 75% percentiles, while the horizontal bars outside the boxes represent the 10% and 90% percentiles. ○ indicates the values outside this range. The RBC adhesion was significantly higher in the group of patients with PV compared with healthy volunteers (***P < .001).