The LDL (Low Density Lipoprotein) is a unit made up of proteins and fats that carry cholesterol in the body. An LDL test measures how much low-density lipoprotein (LDL) you have in your blood. High levels of LDL cholesterol cause a buildup of cholesterol in the arteries, commonly called "bad" cholesterol. High levels of LDL increase the risk of heart disease. An LDL level less than 100 mg/dl is considered optimal, 100 to 129 mg/dl is considered near or above optimal, 130 to 159 mg/dl is considered borderline high, 160 to 189 mg/dl is considered high, and 190 mg/dl or greater is considered very high.