A new analysis recently published in JAMA Internal Medicine adds to the evidence that people may not have to fast before blood tests to check their cholesterol and other lipid levels. Researchers from Brigham and Women's Hospital, Harvard Medical School, and Imperial College in London reviewed data from a study called the Anglo-Scandinavian Cardiac Outcomes Trial–Lipid Lowering Arm (ASCOT-LLA) for their analysis.
Blood tests to check lipid levels, including total cholesterol, LDL cholesterol, HDL cholesterol, and triglyceride levels, are done routinely to help determine a person's risk of heart disease and to decide if and what treatment is necessary. Adults are usually instructed to fast for 9 to 12 hours (often overnight) before these tests, which are typically done together as a lipid panel.
Previous studies have suggested that lipid test results may be equally accurate in determining heart disease risk regardless of whether patients fast or eat, but most of those studies compared fasting and non-fasting results from different individuals. The new analysis compared results of fasting and non-fasting samples drawn four weeks apart from the same individuals with no treatment given during the time between when the two blood samples were drawn. More than 8,000 study participants were included in the analysis. Patients were followed for a median of 3.3 years for major coronary events (e.g., heart attacks, fatal coronary heart disease, stroke, and related deaths.)
The analysis found little difference between the fasting and non-fasting lipid results from the same individuals, according to the authors. The only difference was moderately higher triglyceride levels in non-fasting samples, which was expected. The researchers also found that fasting and non-fasting lipid levels had similar associations with coronary events. Non-fasting lipid levels reflected risk for heart disease similar to fasting levels.
"We hope this study will be the final nail in the coffin, providing strong evidence that, within the same person, fasting or not before a lipid level test doesn't matter for predicting cardiovascular risk," said Samia Mora, MD, MHS, the corresponding author and director of the Center for Lipid Metabolomics at Brigham and Women's Hospital. "This should reassure health care providers and patients that it doesn't make a difference if you fast or don't fast if the goal is to predict your cardiovascular risk."
The analysis is an important one because "[w]e spend most of our lives in a non-fasting state…[a]nd for some patients, especially those who are elderly or have diabetes, it can be risky to fast before lipid testing," said Dr. Mora. "Health care providers held back [on advising against fasting] because of concerns of variability within individuals, but the data here [are] so convincing. It should allow people to feel more comfortable with non-fasting lipid testing for cardiovascular risk assessment, including when taking a statin."
However, an important limitation of the study is the fact that most ASCOT-LLA participants were European, white, and male. The researchers say future studies should look at possible ethnic and racial differences in fasting vs. non-fasting before lipid tests.
Lipid testing without having to fast first would be more convenient and make it easier for patients to comply with getting recommended tests. While some medical societies have endorsed eliminating mandatory fasting before lipid tests, so far this isn't a widely adopted recommendation, so patients should ask their healthcare practitioner what is best for them individually. If other tests that require fasting (e.g., fasting blood glucose) are done at the same time as a lipid panel, then fasting may be still be required.