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Fasting longer than 12 hours before a lab test generally does not provide an advantage over fasting for 8–12 hours, according to new research. A large study of routine outpatient laboratory testing suggests that most tests are minimally affected by the length of time that the patient spends fasting beforehand, potentially changing perspectives on uniform fasting requirements. As published in JAMA Internal Medicine, researchers analyzed 9.8 million test results from 101,148 adults using laboratory data collected between February 2021 and December 2023 from a single hospital in Korea. Although 27 of 121 laboratory measures initially showed fasting-related differences that exceeded established analytical performance specifications, only 10 were confirmed when results from the same patients were compared across different fasting durations.
Glucose testing: In particular, the study found no clinically meaningful glucose difference between fasting 8–12 hours vs more than 12 hours. Most complete blood count, electrolyte, kidney, liver, and cholesterol results also showed little clinically meaningful variation by fasting duration. The results support test-specific rather than universal fasting requirements, the authors note.