According to Human Anatomy at the Online Learning Center, crenation is the contraction of red blood cells when placed in a hypertonic or high-pressure solution, such as salt water. Hemolysis is the explosion or rupturing of red blood cells, when placed in a hypotonic or low-pressure solution, such as water.
Reference.com explains that crenation in cells occurs because the hypertonic solution deprives the cells of water, and causes the cells to take on a scalloped appearance. According to the Virginia Commonwealth University, certain diseases cause crenulated red blood cells, including hepatitis, uremia, malabsorption and a deficiency of pyruvat kinase.
Hemolysis, and its rupture of red blood cells, can result from hemolytic anemia, according to Healthline. This condition causes red blood cells to die at an extraordinary rate, faster than they can be produced. Extrinsic hemolytic anemia occurs because the spleen starts killing red blood cells as a reaction to a bigger health problem, such as leukemia, lymphoma or autoimmune disorders. Intrinsic hemolytic anemia is caused by defective blood cells that the body produces itself. Sickle cell anemia is one example of this type of hemolysis. There are other causes of hemolytic anemia, that range from infections, such as E.coli and streptococcus, to negative reactions to medications. These causes include Wiscott Aldridge syndrome and cancer.