A large study conducted in South Korea has found that fasting for hours before a blood draw makes little difference to results for the vast majority of laboratory tests. Only a handful of measures showed any significant link to fasting time.
The study was led by Sunghwan Shin, a laboratory medicine specialist at Asan Medical Center, affiliated with the University of Ulsan in Seoul. The team carried out a retrospective analysis using data collected at a 670-bed university hospital between 2021 and 2023.
The research drew on more than 9.7 million test results from over 101,000 adult outpatients whose fasting times had been recorded. Participants were divided into three groups based on how long they had fasted: less than 8 hours, 8 to 12 hours, and more than 12 hours.
Out of 121 measures examined, only 10 showed a link between fasting duration and results falling outside the normal analytical range. These included glucose, triglycerides, gamma-glutamyl transferase and lipase, all of which came back higher in patients who had fasted for less than 8 hours.
The authors noted that fasting beyond 12 hours produced no additional significant difference for any of the tests studied. They said the findings support reconsidering the traditional, blanket fasting requirement applied to every test, suggesting instead a more individualized approach tailored to each specific measure.
The researchers pointed out that fasting requirements were first introduced for lipid and glucose tests before being extended to broader test panels. Recommendations have varied between laboratories ever since, they said, partly because systematic data on liver and pancreatic enzymes, blood markers, hormones and vitamins has been scarce.
Liv Tybjærg Nordestgaard, a clinical biochemist at Copenhagen University Hospital, wrote in a commentary accompanying the study that the findings add strong support to a growing body of evidence suggesting fasting before a blood draw is unnecessary.
The study was published in the journal JAMA Internal Medicine.
