Your body produces two main types of cholesterol: low-density lipoprotein (LDL) and high-density lipoprotein (HDL). Elevated LDL levels are a cause of concern due to their role in coronary heart disease and stroke.
HDL, LDL and Triglycerides
Lipoproteins are transporters of lipids (fats) and proteins to and from the liver. Low-density lipoprotein (LDL), known as the "bad" cholesterol, transports lipoproteins through the bloodstream from the liver to the rest of the body. High-density lipoprotein, known as the "good" cholesterol, carries the unsynthesized (unused) fats back to the liver for excretion. Triglycerides are closely associated with cholesterol and move through the blood via particles known as very low density lipoproteins (VLDL).
Testing
For a test to calculate your LDL cholesterol, a blood sample is drawn. You can choose to have two types of testing conducted: total cholesterol, the most common, or a lipid profile test. To ensure accurate results, it is important to not eat at least 12 hours prior to the test and to limit your water intake.
Calculation
A total cholesterol test will show levels for total cholesterol, HDL and triglycerides. Due to the type of expensive and time-consuming processing that needed to accurately measure LDL levels, most cholesterol tests use a calculation to estimate your LDL levels. The Friedewald calculation is LDL = total cholesterol - HDL - (triglycerides/5). All numbers represent the number of milligrams per deciliter (mg/dL) of blood.
For example, test results may show a total cholesterol of 154.1, an HDL value of 43.9 and a triglyceride value of 80.35. Using the Friedwald calculation, your LDL estimate is: LDL = 154.1 - 43.9 - (80.35/5), or 94.13.
Results
Once you have calculated your LDL value, you can determine your risk level. According to guidelines from the American Heart Association, an optimal LDL level is less than 100 mg/dL. A near optimal level ranges between 100 to 129 mg/dL; 130 to 159 mg/dL is borderline high; 160-189 is high; and above 190 is very high.
Exceptions
If your triglycerides are higher than 400 mg/dL, this equation may give inaccurate results so your physician may order a lipid profile test to determine your LDL levels.
