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Is it time to abandon fasting for routine lipid testing?

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Yes. The time has come to change the way we think about fasting before routine lipid testing. We now have robust evidence supporting the routine use of nonfasting lipid testing. Fasting lipid testing is rarely needed, but may be considered for patients with very high triglycerides or before starting treatment in patients with genetic lipid disorders. For most patients, nonfasting lipid testing is appropriate: it is evidence-based, safe, valid, and convenient. More widespread adoption of this strategy by US healthcare providers would improve quality of care and patient and clinician satisfaction.

GUIDELINES HAVE CHANGED

In 2014, the US Department of Veterans Affairs practice guidelines recommended nonfasting lipid testing for cardiovascular risk assessment.1 Other recent clinical guidelines and expert consensus statements from Europe and Canada now also recommend nonfasting lipid testing for most routine clinical evaluations.

Physiologically, we spend most of our lives in the nonfasting state, yet fasting lipid testing was standard practice advocated by earlier clinical guidelines. The rationale for fasting before measuring lipids was to reduce variability and to allow for a more accurate derivation of the low-density lipoprotein cholesterol (LDL-C) concentration using the Friedewald formula. There was also concern that an increase in triglyceride concentrations after consuming a fatty meal would reduce the validity of the results. However, numerous studies have found that the increase in plasma triglycerides after normal food intake is much less than that during a fat-tolerance test, making this less of a concern for most patients.2,3

In addition, recent studies suggest that postprandial effects do not diminish and may even strengthen the risk associations of lipids with cardiovascular disease, in particular for triglycerides.4 Moreover, in certain patients, such as those with metabolic syndrome, diabetes mellitus, or certain genetic abnormalities, fasting can mask abnormalities in triglyceride-rich lipid metabolism, which may only be detected when triglycerides are measured in a nonfasting state. Nonfasting measurements may identify patients with elevated residual risk despite optimal guideline-based treatment.

Guidelines and recommendations that support nonfasting lipid testing
In 2016, a joint consensus statement of the European Atherosclerosis Society and the European Federation of Clinical Chemistry and Laboratory Medicine5 recommended nonfasting lipid testing as the new standard for lipid measurement, with fasting lipid testing considered for patients with triglyceride levels over 400 mg/dL (5 mmol/L). The statement also recommends that nonfasting triglyceride levels greater than or equal to 175 mg/dL (2 mmol/L) should be considered elevated as compared with the 150 mg/dL (1.7 mmol/L) traditionally used for fasting panels.

Recently published recommendations for nonfasting lipid testing for routine assessments are summarized in Table 1.1,5–11

EFFECTS OF THE POSTPRANDIAL STATE ON LIPID LEVELS AND RISK ASSESSMENT

A common concern for clinicians who do not routinely order nonfasting lipid testing is the potential variability in lipid levels and interpretation of these values for treatment decisions. But in most circumstances the differences between fasting and nonfasting measurements are small and are not clinically relevant. Differences in high-density lipoprotein cholesterol (HDL-C) are negligible; slightly lower levels are seen (up to −8 mg/dL) for nonfasting total cholesterol, LDL-C, and non-HDL-C compared with fasting levels; and differences are modest (up to 25 mg/dL higher) for triglycerides.5 These data should reassure clinicians who rely on lipid levels to guide management decisions.9

Cardiovascular risk assessment

Current algorithms for assessing risk of cardiovascular disease use total cholesterol and HDL-C, not triglycerides or LDL-C. Hence, eating has no effect on the risk estimates.

For clinicians who prefer an absolute lipid target for managing risk in patients on lipid-modifying therapy, a nonfasting LDL-C or non-HDL-C (or apolipoprotein B) may be used. The non-HDL-C level is a better risk marker than LDL-C, particularly in patients with low LDL-C or with triglyceride levels of 200 mg/dL or higher.12 Treatment goals for non-HDL-C are 30 mg/dL higher than for LDL-C (fasting or nonfasting). In addition, for these patients with low LDL-C or high triglycerides, a new LDL-C calculation method has more consistent results for fasting and nonfasting values than the commonly used Friedewald calculation.12

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