A study of more than 100,000 adults in Korea found that fasting for less than 8 hours before routine blood tests did not meaningfully change results for the vast majority of lab measures. Researchers analyzed paired within-person samples across 372 test items, comparing results from shorter fasts with those from 8–12 hours and more than 12 hours. Only a few analytes exceeded accepted performance specifications, suggesting that uniform fasting requirements may be unnecessary.
The exceptions were glucose, triglycerides, gamma-glutamyl transferase, and lipase, which were somewhat higher with shorter fasting. For example, glucose was about 13 mg/dL higher with a fast under 8 hours compared with an 8–12 hour fast. The authors noted that clinicians should interpret very short-fasting results carefully for these postprandial-sensitive tests, but prolonged fasting beyond 12 hours offered no measurable advantage for any analyte.
An accompanying editorial called the findings strong support for the growing evidence that fasting blood sampling is not needed for most tests. The editorialists said eliminating fasting requirements could reduce patient burden, simplify clinician instructions, and free up morning clinic resources. However, the study was limited to a single center in Korea, mostly older outpatients, and did not adjust for what patients ate, so the authors and editorialists agreed that broader applicability, especially to younger people and other ethnicities, remains uncertain.