On August 15, 2002 the Clinical Chemistry Laboratory will begin offering a direct measurement of LDL cholesterol as a separate charged test. We will continue to offer the calculated LDL cholesterol at no charge when the combination of cholesterol, triglyceride and HDL cholesterol is ordered. When the patient is fasting and when triglycerides are known to be less than 400 mg/dL, the direct measurement has no advantage over the calculated value. However, if the sample is not obtained in the fasting state, or if triglycerides are known to be greater than 400 mg/dL, then the directly measured LDL is the preferred test. The direct measurement of LDL cholesterol can be performed on samples with triglyceride levels up to 1200 mg/dL. Until measured LDL cholesterol is added to the checkoff requisition, use the “Other Test” request portion of the A1-A requisition and write either “measured LDL” or “direct LDL”. If only “LDL” is written, then the calculated value will be returned. The required sample is serum. A separate tube is not required. Questions can be directed to Dr. Ronald Feld at 6-1759.

References:

Executive summary of the Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). JAMA 285:2486-2497, 2001.

Miller WG, Waymack PP, Anderson FP, et al. Performance of four homogeneous direct methods for LDL-cholesterol. Clin Chem 48:489-498, 2002.

Nauck M, Graziani MS, Bruton D, et al. Analytical and clinical performance of a detergent-based homogeneous LDL-cholesterol assay: a multi-center evaluation. Clin Chem 46:506-514, 2000.

Schectman G, Patsches M, Sasse EA. Variability in cholesterol measurements: comparison of calculated and direct LDL cholesterol determinations. Clin Chem 42:732-737, 1996.