Fasting Adds Little to Lipid Profiles

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Fasting, Nonfasting Tests Each Have Advantages

It had been suggested prior to this study that fasting lipid analysis is not necessarily essential. Measurements of total and HDL cholesterol are affected very little by the nonfasting state, while triglycerides can be affected more substantially.

When triglyceride levels are significantly elevated in the postprandial state, HDL levels may be transiently lower than would be seen after fasting. However, most patients who have normal fasting triglyceride levels do not demonstrate significantly increased postmeal triglycerides. While “calculated” LDL will be affected by transient hypertriglyceridemia, “direct” LDL measurements are not affected by the nonfasting hypertriglyceridemic state.

Patients who have elevated fasting triglycerides may demonstrate significant postmeal triglyceride excursions. Some have advocated the assessment of postmeal triglycerides, since in some patients it is greatly exaggerated compared with the degree of fasting hypertriglyceridemia present, and may correlate more closely with cardiovascular risk and the risk of pancreatitis. Others have not found postmeal hypertriglyceridemia to be more useful than fasting levels in assessing cardiovascular risk.

Patients should have fasting lipid profiles whenever possible, but physicians should consider the periodic assessment of postmeal lipid levels in their patients with hypertriglyceridemia to better understand the degree of triglyceride excursion. Furthermore, in the absence of postmeal hypertriglyceridemia the assessment of total, LDL and HDL cholesterol is valid and constitutes a screening lipid assessment not requiring a return visit. This, however, may not be appropriate for patients whose LDL cholesterol is being tightly or aggressively controlled.

Paul S. Jellinger., M.D., is a clinical endocrinologist in Hollywood, Fla,. and medical editor of Clinical Endocrinology News. He has no relevant disclosures



Hungry mornings – as patients wait to get their fasting blood lipids drawn – may come to an end, based on more evidence that fasting has little meaningful impact on lipid levels and management decisions for most patients.

A review of lipid test profiles drawn from more than 200,000 Calgary residents during 6 months in mid-2011 showed that fasting time prior to the blood draw had little association with lipid subclass levels.

"The results presented herein, combined with those of other recent studies, suggest that nonfasting determination of lipid subclasses is a reasonable alternative to fasting determinations," said Dr. Davinder Sidhu and Dr. Christopher Naugler of the University of Calgary (Alta.), in a report published on Nov. 12 (Arch. Int. Med. 2012 [doi: 10.1001/archinternmed.2012.3708]).

Dr. Christopher Naugler

Fasting lipid measures or direct measurement of low-density lipoprotein (LDL) cholesterol could be considered for patients with an initial triglyceride measurement greater than 400 mg/dL, they added.

"A growing body of evidence from observational studies and statin clinical trials suggests that nonfasting or fasting blood draws may be used for cardiovascular risk assessment and therapeutic decisions," especially when the lipid subfractions of interest are not LDL cholesterol, wrote Dr. Amit V. Khera and Dr. Samia Mora, both from Brigham and Women’s Hospital in Boston, in an invited commentary published online along with the study report (Arch. Int. Med. 2012 Nov. 12 [doi: 10.1001/2013.jamainternmed.263]). Lipid measures that are not very variable by fasting status include total and high-density lipoprotein (HDL) cholesterol, which each varied by less than 2% regardless of fasting duration. LDL cholesterol varied by less than 10%, and triglycerides varied by less than 20%, regardless of fasting duration.

"Given the current lack of evidence for the superiority of fasting lipid testing, it is reasonable to consider nonfasting lipid testing in most individuals who present for a routine clinic visit," said Dr. Khera and Dr. Mora.

They also noted several limitations in the study reported by Dr. Sidhu and Naugler: Most of the blood specimens in the analysis were drawn after at least 9 hours of fasting; because the duration of fasting was not randomized, people who presented to their laboratory nonfasting may differ from those who were fasting in important ways; and the people included in the study were primarily at low risk based on their relatively young age – an average of 53 years – and low total cholesterol level, a mean of 183 mg/dL.

Data for the study came from the records of Calgary Laboratory Services, which is the sole supplier of laboratory services for Calgary, and a population of about 1.4 million people. During the period of April-September 2011, blood samples for lipid measurements were drawn from 209,180 people regardless of fasting duration.

The results of the study suggest that "fasting for routine lipid level determinations is largely unnecessary," concluded Dr. Sidhu and Dr. Naugler.

Dr. Sidhu and Dr. Naugler said they had no disclosures. Dr. Mora disclosed that he has been a consultant to Pfizer and Quest Diagnostics, that he has received speaking honoraria from Abbott, AstraZeneca, and the National Lipid Association, and that he has received research support from AstraZeneca. Dr. Khera had no disclosures.

UPDATED 11/18/12

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