Q&A column

Q. Is it important to fast before a lipid panel?

A.Cholesterol and other lipids are transported in plasma by various lipoprotein particles, including low-density lipoproteins (LDL) and high-density lipoproteins (HDL). While HDL is non-atherogenic and may even be protective, an elevated plasma concentration of the cholesterol carried in LDL (LDL-C) is a well-described risk factor for atherosclerotic cardiovascular disease (ASCVD).

Clinical practice guidelines recommend a target LDL-C level of <100 mg/dL for the primary prevention of ASCVD.¹ Importantly, LDL-C is not typically measured directly in clinical practice. It is more often calculated using the Friedewald formula (calculated LDL-C = total cholesterol − HDL-C − triglycerides/5). Fasting values historically have been recommended to ensure that triglycerides are <400 mg/dL and that accurate calculated LDL-C values are obtained. However, recent studies have confirmed that nonfasting calculated LDL-C values have worth in predicting ASCVD.^2,3 Yet it is now widely recommended that nonfasting non–HDL-C be used for patient management in the general population.

Non–HDL cholesterol, which is calculated by subtracting HDL-C from total cholesterol, encompasses all atherogenic lipoprotein particles and more effectively predicts the risk of major cardiovascular events, including coronary artery disease and stroke, than does LDL-C.^4,5 Additionally, in contrast to LDL-C and triglyceride levels, total cholesterol and HDL-C levels are minimally affected by fasting status.^2,3 Therefore, non–HDL-C can be reliably calculated from nonfasting specimens and the specimens of people with hypertriglyceridemia.

Although cholesterol-reducing agents originally targeted calculated LDL-C, they are now also recommended for managing non–HDL-C in the primary and secondary prevention of ASCVD.⁶ The target non–HDL-C levels for primary and secondary prevention are <130 mg/dL and <100 mg/dL, respectively. These cutoffs are suitable for fasting and nonfasting specimens.⁷

Implementation of non–HDL-C testing in the clinical laboratory involves a simple calculation and no additional assays, and it supports patient care by being convenient for all and ideal for those in whom fasting carries additional risk. Measurement of non–HDL-C is thus simple, robust, and clinically effective, and clinical laboratories should make it widely available for assessing ASCVD risk.

1. Grundy SM, Stone NJ, Bailey AL, et al. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA guideline on the management of blood cholesterol: a report of the American College of Cardiology/American Heart Association Task Force on clinical practice guidelines. Circulation. 2019;139(25):e1082–e1143.
2. Langsted A, Freiberg JJ, Nordestgaard BG. Fasting and nonfasting lipid levels: influence of normal food intake on lipids, lipoproteins, apolipoproteins, and cardiovascular risk prediction. Circulation. 2008;118(20):2047–2056.
3. Sidhu D, Naugler C. Fasting time and lipid levels in a community-based population: a cross-sectional study. Arch Intern Med. 2012;172(22):1707–1710.
4. Boekholdt SM, Arsenault BJ, Mora S, et al. Association of LDL cholesterol, non-HDL cholesterol, and apolipoprotein B levels with risk of cardiovascular events among patients treated with statins: a meta-analysis. JAMA. 2012;307(12):1302–1309.
5. Brunner FJ, Waldeyer C, Ojeda F, et al. Application of non-HDL cholesterol for population-based cardiovascular risk stratification: results from the Multinational Cardiovascular Risk Consortium. Lancet. 2019;394(10215):2173–2183.
6. Expert Dyslipidemia Panel, Grundy SM. An International Atherosclerosis Society position paper: global recommendations for the management of dyslipidemia. J Clin Lipidol. 2013;7(6):561–565.
7. Guo LL, Chen YQ, Lin QZ, et al. Non-HDL-C is more stable than LDL-C in assessing the percent attainment of non-fasting lipid for coronary heart disease patients. Front Cardiovasc Med. 2021;8:649181.

Andy Hoofnagle, MD, PhD
Professor, Laboratory Medicine
Head, Division of Clinical Chemistry
Department of Laboratory Medicine and Pathology
University of Washington, Seattle, Wash.
Chair, CAP Accuracy-Based
Programs Committee

Rebecca Treger, MD, PhD
Clinical Pathology Resident
University of Washington, Seattle, Wash.
Junior Member, CAP Accuracy-Based Programs Committee

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