Catheter-induced clotting in platelet-poor plasma. Pooled platelet-poor plasma was incubated in wells of a 96-well plate at 37°C in the absence (open circles) or presence of PCI catheter segments (closed circles). After the addition of CaCl2 to 20mM, absorbance was monitored at 340 nm at 10-second intervals, and the values were plotted versus time. A well from a separate plate at 37°C was photographed at 30-second intervals, and individual images at 4 time points (labeled i-iv) are displayed above the plot. The arrow identifies the catheter segment. With increasing incubation times, an opaque clot forms on the catheter segments positioned at the periphery of the well and then extends to fill the center of the well.