Low-density lipoprotein particles, commonly known as LDL cholesterol, has become the number to watch on cholesterol tests. Total cholesterol, studies have shown, is far less important than the breakdown of LDL, considered the "bad" form of cholesterol and high-density cholesterol, or HDL, considered the "good" cholesterol in your blood. A blood test called a lipid panel measures the levels of total cholesterol, HDL, LDL and triglycerides. The LDL level is difficult to determine directly, so a formula using the HDL and triglyceride levels estimates your DLD level.
Function
Both LDL and HDL transport cholesterol through your blood, because cholesterol, a waxy substance, doesn't dissolve in blood and can't travel through it. Lipoproteins package cholesterol, triglycerides and other substances in their core and transport cholesterol, an essential substance for life, to cells. Low-density lipoproteins carry between 60 and 70 percent of cholesterol, Harvard Health Publications states.
Problems
Low-density cholesterol in itself is necessary and not "bad". It's only bad if there's too much of it in your blood, because excess LDL begins to oxidize, or break down into harmful substances that can infiltrate damaged areas on the inside of the blood vessel walls, causing inflammation that leads to atherosclerosis.
Determination
Because LDL is difficult to measure directly, it's estimated using the HDL and triglyceride levels, which are easier to determine in a blood sample, Hooper Holmes Laboratories explains. A fasting blood sample is necessary, because eating before the tests causes triglycerides to rise and can change the LDL estimation. The Friedewald formula is: LDL = Total Cholesterol - HDL - 1/5 triglycerides. The formula is accurate only if triglyceride levels are lower than 400 mg per deciliter, or mg/dL. For example, if your total cholesterol is 200 and your HDL is 60, 200 - 60 = 140. If your triglycerides are 200, divide by 5, which equals 40. Now subtract 140 - 40 = 100. Your LDL is 100.
Norms
Normal LDL levels should optimally fall below 70 mg/dL if you're at high risk of heart disease. Below 100 mg/dL is ideal and between 100 and 129 mg/dL is near ideal for healthy people. Between 130 and 159 mg/dL is classified as borderline high, 160 to 189 mg/dL as high and over 190 mg/dL as high, according to MayoClinic.com
Reducing LDL
While diet can play a part in cholesterol levels, 75 percent of the cholesterol is manufactured in your liver and other cells. While you can't change your heredity, a factor in how your body manufactures cholesterol, modifying your diet and making lifestyle changes like quitting smoking, exercising 30 minutes a day, reducing your weight if you're overweight and keeping blood glucose levels under control all help lower LDL levels.
