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How Is LDL Cholesterol Calculated?
Cholesterol levels are measured in milligrams (mg) of cholesterol per deciliter (dL) of blood in the US and some other countries. Canada and most European countries measure cholesterol in millimoles (mmol) per liter (L) of blood.
Blood tests typically report LDL-C. These numbers are usually based on calculation, using the
Friedewald equation that includes total cholesterol, HDL-C, and triglycerides. This equation relies on the assumption that the ratio of triglyceride to cholesterol is constant,
which is not always the case.
If mg/dl is your unit, like in the United States the formula looks like this:
LDL cholesterol = [Total cholesterol] – [HDL cholesterol] – [TG]:5
If mmol/l is your unit like in Australia, Canada, and Europe the formula looks like this:
LDL cholesterol = [Total cholesterol] – [HDL cholesterol] – [TG]:2.2
Thus, LDL-C calculations may have limitations when blood triglyceride levels are either high or low.
Direct LDL -C measurements are also available, but are less often done due to higher costs.
Some studies show that the number of LDL particles (
LDL-P) may be a better predictor of risk than LDL-C. LDL particle size may also be important when assessing risk."