LDL-C is most often measured indirectly, using a calculation based on other blood lipid analytes. Historically, the Friedewald calculation2 has been the most common approach. This equation, developed in the 1970s, incorporates total cholesterol, HDL-cholesterol (HDL-C), and triglyceride concentrations:
LDL-C (mg/dL) = total cholesterol – HDL-C – (triglycerides/5),
where “triglycerides/5” is used to represent very low-density lipoprotein-C (VLDL-C).
LDL-C concentration can also be measured directly or with newer equations. Quest Diagnostics uses the Martin-Hopkins calculation, as described below, which provides accurate quantitation even in patients with triglyceride (TG) values between 200 mg/dL and 400 mg/dL and LDL-C levels below 70 mg/dL.