South Korea: Researchers have found in a new cross-sectional observational study that fasting for less than 8 hours before routine blood tests generally had minimal impact on most laboratory results, challenging the need for prolonged fasting before testing.

However, glucose and a few other laboratory parameters were higher with shorter fasting durations. They noted that fasting has traditionally been recommended to minimize preanalytical variation in laboratory measurements.
The study predominantly involved older patients at a single centre in South Korea, limiting the generalizability of its findings.
The study, published in JAMA Internal Medicine, was conducted by Sunghwan Shin, Department of Laboratory Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, and colleagues. The researchers investigated whether fasting duration was associated with clinically meaningful differences across a wide range of routine laboratory tests.
The retrospective analysis included 101,148 adult outpatients who underwent blood testing at a 670-bed university hospital in Seoul between February 2021 and December 2023. The researchers examined 9,755,547 test results across 372 laboratory test items. Fasting duration was classified into three groups: less than 8 hours, 8–12 hours, and more than 12 hours.
The team used statistical models adjusted for age, sex, and clinical department to compare laboratory results across fasting groups. They also conducted within-person analyses of patients who underwent repeated testing to account for differences between individuals.
The findings revealed the following:
  • Differences exceeding established analytical performance specifications were observed in 27 of 121 analytes in comparisons between fasting groups. However, only 10 analytes showed consistent differences in paired within-person analyses.
  • Glucose, triglycerides, gamma-glutamyl transferase (GGT) and lipase levels were higher among patients fasting for less than 8 hours, with differences of 10.8%, 20.1%, 14.8% and 36.4%, respectively.
  • No analyte showed a difference exceeding the established performance threshold between patients fasting for 8–12 hours and those fasting for more than 12 hours.
  • Within the group fasting for less than 8 hours, glucose and lactate concentrations declined as fasting duration increased, while lipid levels showed no significant linear trend.
The researchers noted limitations, including the retrospective, single-centre design, reliance on unverified fasting durations, and lack of data on meal composition. Time of day, medication changes and intercurrent illness may also have influenced results. The study did not assess whether fasting-related differences crossed clinical decision thresholds, and its older population limits generalizability to younger adults.
The findings support test-specific fasting requirements rather than uniform recommendations. Fasting for at least 8 hours may be necessary for accurate glucose and lipid measurements, while shorter fasting may suffice for many other tests. Fasting beyond 12 hours offered no additional measurable benefit for any analyte.
The authors concluded that flexible, analyte-specific fasting protocols could reduce patient burden while maintaining test accuracy. Prospective multicentre studies are needed to confirm these findings across diverse populations.
Reference:
Shin S, Kim S, Yu S, et al. Fasting Duration and Differences Across Routine Laboratory Tests. JAMA Intern Med. Published online September 28, 2026. doi:10.1001/jamainternmed.2026.4718


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Article Source : JAMA Internal Medicine

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Medha Baranwal

Medha Baranwal holds a Bachelor’s degree in Biomedical Sciences from the University of Delhi and a Master’s degree in Biotechnology from Amity University. Since May 2018, she has been contributing to Medical Dialogues, writing and editing medical news articles that translate complex research into clear, accessible information for healthcare professionals.

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