November 12, 2012
Requiring a patient to fast for many hours before a lipid test may soon be a thing of the past.
Although present guidelines encourage doctors to test for total lipids and lipid subclass levels only when a patient has fasted for more than 8 hours, a report published online November 12 in Archives of Internal Medicine found that there may no longer be a need for a patient to fast. There is very little difference in lipid levels when measured in a fasting or nonfasting state, according to the research.
"The incremental gain in information of a fasting profile is exceedingly small for total and HDL [high-density lipoprotein] cholesterol values and likely does not offset the logistic impositions placed on our patients, the laboratories, and our ability to provide timely counseling to our patients," J. Michael Gaziano, MD, writes in an accompanying editorial. "This, in my opinion, tips the balance toward relying on nonfasting lipid profiles as the preferred practices," writes Dr. Gaziano, who is with the Department of Medicine at Veterans Affairs Boston Healthcare System, Brigham and Women's Hospital, and Harvard Medical School, Boston, Massachusetts.
Two other doctors agree. "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," Amit Khera, MD, and Samina Mora, MD, write in asecond editorial. Dr. Khera is with the Division of Internal Medicine and Dr. Mora is with the Department of Preventive Medicine and Cardiovascular Disease at Brigham and Women's Hospital and Harvard Medical School.
A few prior studies have also suggested that measuring all lipid subclasses when the patient has not fasted will produce acceptable results — even beneficial results in some cases because some nonfasting markers are better predictors of future cardiac events, study authors note. Most of those studies, however, had the limitation of pertaining only to certain groups of patients.
"Therefore, there was a need for a large-scale study of the association of fasting time with lipid levels in an unselected population," study authors Davinder Sidhu, MD, LLB, and Christopher Naugler, MSc, MD, Department of Pathology and Laboratory Medicine, University of Calgary, Alberta, Canada, write.
To investigate the relationship between fasting duration and lipid levels in a large community-based population, the authors designed the study as a cross-sectional analysis of laboratory data.
They used secondary data from Calgary Laboratory Services and examined the test results of every individual with lipid test panels between April 1, 2011, and September 30, 2011.
A policy change in 2011 allowed the laboratory to process samples for fasting lipid levels regardless of the duration of fasting time.
Fasting times ranged from 1 hour to more than 16 hours. Lipid results included the mean levels of HDL cholesterol, low-density lipoprotein (LDL) cholesterol, total cholesterol, and triglycerides. A total of 209,180 participants were included in the analysis. Authors used linear regression models to project average cholesterol levels at various fasting times.
The study found that variation among mean cholesterol subclass levels was less than 2% for total cholesterol and HDL cholesterol, less than 10% for calculated LDL cholesterol, and less than 20% for triglycerides among individuals with various fasting times. Only a minority of fasting intervals had statistically significant differences among cholesterol subclasss levels.
"While there are some circumstances in which a fasting level may be useful, most of the time it is probably not necessary," Dr. Gaziano stresses in his editorial.
But the study is not without limitations, he writes.
"The analyses assume that there is no systematic bias introduced by the timing of the blood draw, " Dr. Gaziano notes in his editorial. "No information was available on medications or repeated measures. More data by age would have been helpful," he says.
Other limitations, according to the authors, are that the study did not examine individual meal choices before testing or control for recall errors of self-reported fasting time.
Future research, the authors suggest, should involve "examining repeated measurements with differing fasting times in the same individuals."
Arch Intern Med. Published online November 12, 2012. Full text Gaziano commentary Khera and Mora commentary
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