ABSTRACT & COMMENTARY
LDL Levels — Are Fasting Blood Specimens Necessary?
By Harold L. Karpman, MD, FACC, FACP
Clinical Professor of Medicine, UCLA School of Medicine
Dr. Karpman reports no financial relationships relevant to this field of study.
Nonfasting LDL-C has a similar prognostic value to that of fasting LDL-C with respect to both all-cause and cardiovascular mortality.
Doran B, et al. Prognostic value of fasting versus nonfasting low-density lipoprotein cholesterol levels on long-term mortality: Insight from the National Health and Nutrition Examination Survey III (NHANES-III). Circulation 2014;130:546-553.
Current national and international guidelines on cholesterol management recommend that lipid panel measurements be performed after an 8- to 12-hour fast,1-3 presumably to obtain more accurate values of certain lipid parameters, especially the triglyceride levels. Published data have demonstrated that the levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol vary only minimally with respect to the difference between fasting vs nonfasting specimens, whereas triglycerides may vary by up to 20-30%.4,5 Furthermore, recent studies have suggested that nonfasting lipid values may be equivalent or even superior to predicting cardiovascular outcomes, presumably because the nonfasting state may more accurately reflect the degree of the body’s exposure to circulating lipids.6-8
Doran and her associates analyzed the National Health and Nutrition Examination Survey III (NHANES-III), a nationally representative database of the U.S. population, to evaluate the prognostic value of fasting vs nonfasting LDL-C for prediction of all-cause mortality and cardiovascular mortality in men and women.9 If participants were unable to attend an examination at a selected center, they were interviewed in their homes and examined in a mobile examination center where blood samples were obtained and physical examinations were performed. Propensity score matching was used to assemble fasting and nonfasting cohorts with similar baseline characteristics. The primary outcome measured was all-cause mortality and the secondary outcome was cardiovascular mortality. The final dataset included 16,161 individuals, which yielded 4299 pairs of fasting and nonfasting participants, and the mean follow-up period was 14 years. The results revealed that the nonfasting LDL-C values had a prognostic value similar to that of the fasting LDL-C values.
COMMENTARY
The recently published 2013 American College of Cardiology/American Heart Association guidelines recommend obtaining fasting blood specimens when lipids are being evaluated, even though published studies10,11 have demonstrated little variation between postprandial LDL-C levels compared with fasting levels. Requiring patients to fast before blood is obtained may result in increasing anxiety and stress, potential hypoglycemia in patients with diabetes mellitus, and potential missed days of work associated with increased transportation costs. The inconvenience of fasting may also delay treatment or diagnosis of hyperlipidemia if patients are unable to fast before clinic visits. Therefore, the results of the current study are important as they demonstrate that fasting is not required to obtain lipid values that are accurate and appropriate for clinical use.9 From a practical point of view, if nonfasting lipid values demonstrate abnormal lipid values to be present, especially high triglycerides, a repeat fasting study would be recommended to determine whether triglycerides are truly elevated, which may require specific drug therapy. Obviously, enabling patients to obtain nonfasting lipid profiles would improve patient satisfaction and potentially avoid delays in detection and treatment of hyperlipidemia while at the same time providing prognostic value similar to that of a nonfasting LDL-C value.
In summary, the Doran study fails to demonstrate that fasting LDL-C values have a superior prognostic value when compared to nonfasting LDL-C values for the prediction of both all-cause and cardiovascular mortality.9 In addition, the study also suggested that fasting TC and triglyceride levels do not improve prognostic significance over nonfasting levels. National and international cardiac organizations may have to consider changing the current recommendation that lipid values be obtained preferably from fasting blood specimens.
REFERENCES
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9. Doran B, et al. Prognostic value of fasting versus nonfasting low-density lipoprotein cholesterol levels on long-term mortality: Insight from the National Health and Nutrition Examination Survey III (NHANES-III). Circulation 2014;130:546-553.
10. Langsted A, et al. Fasting and nonfasting lipid levels: Influence of normal food intake on lipids, lipoproteins, apolipoproteins and cardiovascular risk prediction. Circulation 2008;118:2047-2056.
11. van Dieren S, et al. Nonfasting lipids and risk of cardiovascular disease in patients with diabetes mellitus. Diabetologia 2011;54:73-77.
