HDL usually fluctuates from 1.08-1.91 mmol/L and it is recommended that it should not be less than 1.0 mmol/L. HDL, also known as high-density lipoprotein, is the good lipoprotein among the four brothers of blood lipids. The four brothers of blood lipids, including total cholesterol, triglycerides, LDL cholesterol and HDL cholesterol. HDL is the good lipoprotein and is the “scavenger” in blood vessels, as it allows lipids that have been deposited in blood vessels to be transported back to the liver for further utilization. LDL cholesterol, on the other hand, is a bad lipoprotein cholesterol, which causes the intima of the arteries and atherosclerosis to grow plaques. If the plaque ruptures, a blood clot will be formed locally, and plaque dislodgement may also cause distant embolism. Elevated LDL cholesterol is a factor of atherosclerosis, which is an important factor in causing heart attack, brain attack and various atherosclerotic diseases.