Plate Nº 61 · recorded October 10, 2026
Health & Medicine ResearchReported finding
Fasting Before Blood Tests: Only 10 of 121 Tests Really Need It
A JAMA Internal Medicine study of 101,148 adults found only 10 of 121 routine blood tests changed meaningfully when patients fasted less than 8 hours.
By Priya Raman3 min read659 words
In brief
- Researchers analyzed data from 101,148 adults across 670 South Korean hospitals, screening nearly 10 million test results.
- Only 10 of 121 routine tests exceeded clinical error thresholds when fasting lasted under 8 hours.
- Glucose was 10.8% higher, triglycerides 20.1% higher and lipase 36.4% higher with fasting under 8 hours.
- Fasting beyond 12 hours made no clinically meaningful difference to any test result.
- The study was published in JAMA Internal Medicine in 2026.
Out of 121 routine laboratory tests, only 10 changed enough to matter clinically when patients had fasted for less than 8 hours. That is the central finding of a large South Korean study, published in JAMA Internal Medicine, which suggests the blanket instruction to fast before nearly every blood test may be unnecessary for most people.
Many clinics still ask patients to avoid food for 8–12 hours before a blood draw. The rule was originally designed for glucose and lipid testing, but over time it became the default for almost all routine blood panels. Researchers led by Sunghwan Shin set out to test whether that habit still makes sense.
What did the study measure?
The team screened nearly 10 million test results collected from 670 hospitals across South Korea, ultimately analyzing data from 101,148 adults. Based on the time since each patient's last meal, as documented by the phlebotomist, they sorted people into three groups: fasted for less than 8 hours, 8–12 hours, or more than 12 hours.
To rule out the possibility that differences in patients' health drove the results, the researchers compared the same individuals across separate visits, each with a different fasting duration. This within-person design makes the findings more robust than a simple snapshot comparison between different patients.
Which tests actually change without fasting?
Most results stayed stable regardless of fasting. Blood counts, kidney function markers, electrolytes and most liver enzymes came out the same whether patients had eaten recently or not.
Only a handful of tests showed meaningful differences when patients fasted for less than 8 hours:
- Blood glucose ran 10.8% higher
- Triglycerides, a type of fat in the blood, ran 20.1% higher
- Lipase, a digestive enzyme made by the pancreas, ran 36.4% higher
Glucose then fell steadily with longer fasting, dropping by roughly 4.3 mg/dL for each additional hour without food.
Does fasting longer than 12 hours help?
No. Whether patients fasted for 8–12 hours or pushed past 12 hours made no clinically meaningful difference to any test result. Extending the fast added nothing to accuracy, the researchers found, and simply caused patients extra discomfort.
Why does this matter beyond the lab?
People spend most of their day in a nonfasting state, so nonfasting tests may actually reflect a person's habitual physiology better than fasting samples do. Fasting also creates practical problems. Patients often cannot get blood drawn the same day a test is ordered and must make a separate visit. Early-morning fasting draws can pile extra demand onto hospitals and laboratories. Unless fasting offers a clear clinical advantage for a specific test, those costs may outweigh the benefits.
The study also addresses a genuine gap in the evidence. Previous research on fasting before blood tests focused heavily on cholesterol and triglyceride testing, leaving little data for the many other tests doctors order routinely.
What are the limitations?
The findings come from retrospective analysis of real-world hospital data, not from a controlled experiment. And the study population was South Korean, so the results may not transfer directly to other groups. The authors themselves say further research involving more diverse populations is needed before clinical standards can be redefined.
Still, the practical implication is clear. The researchers propose replacing the one-size-fits-all fasting rule with test-specific requirements, since fasting duration genuinely mattered for only a small fraction of routine tests — chiefly glucose, triglycerides, lipase and a few liver markers. An accompanying editorial in the same journal, authored by Liv Tybjærg Nordestgaard and colleagues and titled "Time to Stop Fasting Before Blood Sampling," signals that the question is now firmly on the table in clinical medicine.
For patients, the takeaway is not to skip fasting instructions on your own. Until guidelines change, follow your clinician's advice — but expect the 8–12 hour rule to come under growing scrutiny, and only for the tests where it demonstrably counts.
via Medical Xpress (Source)
More from Priya Raman
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Senior reporter covering industry trends and analytics at SciBeat.
207 articles
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