Is it time to abandon fasting for routine lipid testing?
EVIDENCE SUPPORTING NONFASTING LIPID TESTING
The adequacy of nonfasting lipid testing for general screening for cardiovascular disease has been verified in large prospective studies over the past several decades.2,13,14 These studies evaluated cardiovascular event and mortality rates and found consistent associations of nonfasting lipid levels with cardiovascular disease. Studies that included both fasting and nonfasting patient populations found similar or occasionally even greater cardiovascular risk associations for nonfasting lipid measurements (including for LDL-C and triglycerides) compared with fasting lipid measurements.
The Emerging Risk Factors Collaboration14 reviewed the data from 68 studies in more than 300,000 people and found that the relationship between lipid levels and incident cardiovascular events was just as strong when nonfasting lipid values were used. In fact, at least 3 large statin trials reviewed (a total of 43,000 people) used nonfasting lipids.14
Genetic studies using mendelian randomization have also linked nonfasting triglyceride levels (and remnant cholesterol) to an increased risk of cardiovascular events and of death from any cause.15,16
Therefore, the evidence overall suggests that nonfasting lipid measurements are acceptable with respect to risk assessment, and indeed may be preferred in most instances, especially in patients with an atherogenic metabolic milieu that may otherwise be masked by the fasting state.
OTHER BENEFITS OF NONFASTING LIPID TESTING
Nonfasting lipid panels are more economical and safer for certain groups, such as elderly or diabetic patients. A pilot study17 found that up to 27.1% of patients with diabetes reported experiencing a fasting-evoked hypoglycemic event en route to testing because of fasting for blood work. These events are vastly underreported and add to patient morbidity that can easily be avoided by adopting nonfasting lipid testing.
No study has assessed the cost-effectiveness of fasting vs nonfasting lipid testing. It is common for patients to present for their office appointment without having obtained a fasting lipid panel simply because they forgot to fast and were turned away by the laboratory. Thus, management decisions during the visit are often deferred, and patients must return to the laboratory and reschedule follow-up visits. This is inefficient, increases outpatient waiting times, and also potentially deprives others of access to needed care. Laboratory workflow can also suffer from an influx of early morning visits for fasting tests, decreasing system efficiency. Decreased efficiency in multiple levels of the healthcare system leads to increased costs, burden on healthcare providers, and decreased patient and physician satisfaction.
GETTING WITH THE GUIDELINES
The 2002 National Cholesterol Education Program expert panel report18 and the 2013 joint cholesterol guidelines of the American College of Cardiology and the American Heart Association9 both recommended that initial screening should involve fasting lipid testing, but they also allowed measuring nonfasting total cholesterol, HDL-C, and non-HDL-C.18 And internationally, there has been a shift in practice recommendations toward nonfasting lipids over the past 10 years (Table 1).
In 2014, the US Department of Veterans Affairs, the UK National Clinical Guideline Centre, and the Joint British Societies said that fasting is no longer needed for routine testing.10 In 2016, the European Atherosclerosis Society and the European Federation of Clinical Chemistry and Laboratory Medicine recommended nonfasting lipid testing as the standard of care and provided clinically useful cut points for both fasting and nonfasting lipid measurements.5
In most guidelines, the threshold for elevated nonfasting triglycerides was defined as 175 mg/dL (≥ 2 mmol/L) or greater, and this level has been validated prospectively in a large study of US women.5,19 Repeat measurement of fasting triglycerides may be considered when nonfasting levels are greater than 400 mg/dL,5 although there is no consensus in the guidelines regarding when or if fasting triglycerides should be remeasured. (In the Danish experience,5 only 10% of patients have required repeat fasting values). In addition, the 2016 Canadian Hypertension Education Program guidelines6 removed fasting as a requirement. The 2016 Canadian Cardiovascular Society dyslipidemia guidelines7 reported that nonfasting lipid testing is a suitable alternative to fasting. Furthermore, the most recent revision of the European Society of Cardiology dyslipidemia guidelines8 acknowledged that nonfasting lipid panels are acceptable for screening and management of patients without severe hypertriglyceridemia or those with extremely low LDL-C levels.
LIMITATIONS OF THE EVIDENCE
To date, no study has assessed the predictive value of fasting vs nonfasting lipid measurements in the same individuals, and there have been no randomized outcomes trials or cost-effectiveness analyses. Ethnic variations in lipoproteins and nonfasting status also need to be investigated as nonfasting lipid testing becomes more universally accepted.
TAKE-HOME POINTS
- Robust evidence supports the routine use of nonfasting lipid testing, with fasting panels reserved potentially for patients with very high triglycerides and before starting treatment in those with genetic lipid disorders.
- For most patients, nonfasting tests are evidence-based, safe, valid, and convenient.
- More widespread adoption of this strategy by US healthcare providers would improve both quality of care and patient-clinician satisfaction.
