Fasting Before Lipid Testing: What’s All the Hype?
According to the third report of the National Cholesterol Education Program (NCEP) published in JAMA 2001, blood samples for lipid profiles should be obtained after a 9 – 12 hour fast. It is well known that lipid testing is paramount in cardiovascular risk stratification, but it is not practical for all patients to be fasting for this long. More importantly, patients may just forgo testing all together, due to the lack of transportation or additional resources required to return to the lab in a fasting state.
In the Sidhu et al study 209,180 patients were evaluated in a cross-sectional study of lipid panels versus time of fasting over a 6-month period. The total cholesterol and high-density lipoprotein cholesterol levels differed little among individuals with various fasting times. LDL cholesterol had up to 10% variation and TG had up to 20% variation. A few limitations of this study were fasting duration was not randomized, the population was relatively young (mean, 53 years), and the total cholesterol levels were low (mean, 183mg/dL) reflecting a low risk population.
Another study by Lund SS et al published in 2011 looking at 74 patients with type 2 DM looked at lipid profiles at 1.5, 3.0, 4.5, and 6.0 hours after eating a meal. What they found was that LDL on average was 34mg/dL lower than fasting levels using three different methods of testing. Furthermore, 38% of patients with diabetes mellitus and >50% of patients on statins were reduced to lower levels of the Adult Treatment Panel III risk categories. Even though this is a small study, its findings raise a potential concern that measuring non-fasting LDL levels may be falsely reassuring in patients with diabetes mellitus or on statins.
In a prospective study of 26,330 healthy women associations of baseline lipids with incident cardiovascular disease were examined over an 11-year follow-up. LDL concentrations differed minimally (1 – 5% different) for fasting versus non-fasting patients, but triglycerides were higher in the non-fasting women by approximately 15%. A first cardiovascular event was seen in 3.8% (fasting) versus 3.3% (non-fasting) of women, but statistical analysis showed that non-fasting levels were not statistically significant. Triglyceride levels had a stronger association with incident cardiovascular disease.
Langsted et al cross-sectionally studied 33,391 patients and compared fasting levels versus non-fasting levels of lipids. HDL was decreased by 4mg/dL, LDL increased up to 8mg/dL, and triglyceride levels were increased up to 27 mg/dL in the non-fasting state. More importantly, the non-fasting lipids still predicted risk of cardiovascular events.
Finally, The Emerging Risk Factors Collaboration looked at 302,430 patients without vascular disease and took 20 studies (103,354 patients) with non-fasting levels of lipids and looked at their relationship with cardiovascular events. They found that assessment could be simplified by measurement of either total or HDL cholesterol levels without the need to fast and without regard to triglyceride.
In my opinion, how this affects your practice:
- Currently, a fasting lipid testing strategy is not superior to non-fasting lipid testing strategy
- It is reasonable to consider a non-fasting lipid testing strategy in most healthy individuals
- Do not use non-fasting lipid testing in patients with hypertriglyceridemia (>400mg/dL), patients on statins, and patients with diabetes mellitus
- Be careful using non-fasting lipid testing for cardiovascular risk stratification
References: 1. Di Angelantonio E et al. Major Lipids, Apolipoproteins, and Risk of Vascular Disease. JAMA 2009; 302 (18): 1993 – 2000. PMID: 19903920 2. Langsted A et al. Fasting and Nonfasting Lipid Levels: Influence of Normal Food Intake on Lipids, Lipoproteins, Apolipoproteins, and Cardiovascular Risk Prediction. Circ 2008; 118: 2047 – 2056. PMID: 18955664 3. Lund SS et al. Agreement Between Fasting and Postprandial LDL Cholesterol Measured with 3 Methods in Patients with Type 2 Diabetes Mellitus. Clinical Chem 2011 Feb; 57 (2): 298-308. PMID: 20947697 4. Mora S et al. Fasting Compared With Nonfasting Lipids and Apolipoproteins for Predicting Incident Cardiovascular Events. Circ 2008; 118: 993 – 1001. PMID: 18711012 5. Sidhu D et al. Fasting Time and Lipid Levels in a Community-Based Population. Arch Intern Med 2012; 172 (22) 1707 – 1710. PMID: 23147400 _______________________________________________________________________________
Dr. Salim R. Rezaie is a physician at the University of Texas Health Science Center at San Antonio. He is double board-certified in Emergency Medicine and Internal Medicine.