In addition, when sickle cell disease patients experience a painful crisis, there is evidence that the platelet activation and abnormal blood clotting increase even further. Activated platelets release a substance called cluster of designation 40 ligand, which can increase how sticky the lining of blood vessels are and can increase the abnormal blood clotting. The level of cluster of designation 40 ligand is much higher in sickle cell disease patients compared to healthy individuals without this disease. In addition, the levels increase even further when sickle cell patients are experiencing a painful crisis.