Low HDL refers to low HDL cholesterol. Low HDL cholesterol indicates that the patient has abnormal blood lipids, which is a type of hyperlipidemia. HDL can protect the blood vessels of human body and is good for human blood vessels. If HDL is low, the patient is prone to atherosclerosis forming plaques. Hyperlipidemia includes low HDL cholesterol, high LDL cholesterol, hypertriglyceridemia, and hypercholesterolemia. Patients with hyperlipidemia start with dietary and lifestyle modifications to lower their blood lipids. After three months, if the lipids still cannot be reduced to normal, lipid-lowering medication should be taken.