The direct low-density lipoprotein cholesterol test (direct LDL-C) measures the amount of LDL cholesterol, sometimes called “bad” cholesterol, in the blood. Elevated levels of LDL-C are associated with an increased risk of hardening of the arteries (atherosclerosis) and heart disease.
For the direct determination of LDL cholesterol in nonfasting patients or in patients whose fasting triglycerides are >400 mg/dL, where the estimation of LDL by calculation may not be possible or may lead to inaccuracies. LDL cholesterol measurement, in conjunction with other lipid measurements, has been shown to be useful in assessing the risk of coronary heart disease (CHD). The National Cholesterol Education Program (NCEP) has stated that LDL cholesterol should be the key index in determination of CHD risk. Laboratory estimation of LDL cholesterol is most commonly determined by the use of formulas, such as the Friedewald formula. Use of this formula is limited to fasting samples with triglycerides <400 mg/dL. Triglyceride values between 250-400 mg/dL may also be associated with errors in LDL cholesterol estimation by calculation which, in turn, can lead to misclassification of the patient in regard to the NCEP guidelines.