The danger of having a high cholesterol ratio is that the coronary arteries can harden and narrow, thus increasing the chance of a heart attack or a stroke, according to WebMD. A patient's cholesterol is measured with a blood test, and the ratio is determined by dividing her total cholesterol by her high-density lipoprotein, or HDL. Total cholesterol is the sum of the patient's HDL, low-density lipoprotein, or LDL, and 20 percent of her triglycerides, states the American Heart Association.
The AHA recommends using total cholesterol levels instead of cholesterol ratios to guide patient care, explains WebMD. High cholesterol damages the endothelium, or inner lining of the artery, which creates the conditions that lead to atherosclerosis. As of 2015, the prevailing theory is that the fatty acids in LDL damage the walls of blood vessels through oxidation, so more LDL in the blood causes more damage.
However, a high HDL level is correlated with a reduced risk of atherosclerosis and heart attacks. HDL reduces inflammation in arteries that have been damaged, blocks the oxidization of LDL and is reported to remove some LDL from the cells in the arterial wall and transport it to the liver, which breaks it down.