The appropriate level of HDL in normal people is >1mmol/L, so HDL 1.91mmol/L is normal. HDL belongs to a group of lipoproteins with the largest particle density in human serum, and the increase of this lipoprotein is beneficial to transfer the cholesterol from the surrounding tissues to the liver for recirculation or excretion in the form of bile acids, which can prevent atherosclerosis from occurring, and it belongs to the anti-atherosclerotic factor, and the high level has an important role in the prevention of coronary heart disease. If the physical examination finds that the HDL value is abnormal, the cause of the disease should be clarified under the guidance of the doctor and actively treated.