Serum LDL usually refers to low-density lipoprotein cholesterol (LDL-C), a lipid test it is a cholesterol-rich lipoprotein containing protein, phospholipids, and cholesterol, which enables the formation of atheromatous plaques in the arterial wall, and elevated LDL cholesterol is one of the risk factors for atherosclerosis. Currently, the reference range of LDL in serum is ≤3.4mmol/L. If the range is 3.4-4.lmmol/L, it is a borderline level, and if it is >4.1mmol/L, it is an elevated state. In general, elevated LDL cholesterol is usually seen in patients with diabetes mellitus, hypothyroidism, hyperlipoproteinemia, nephropathy, obstructive jaundice, hypercholesterolemia, and also in people with gestational obesity, high-calorie diets, and low physical activity. If LDL cholesterol is decreased, it may be caused by conditions such as hypo-beta-lipoproteinemia, anabolic lipoproteinemia, cirrhosis, malabsorption syndrome, hyperthyroidism, and chronic adrenocortical insufficiency.