Fasting Before Blood Tests Might Not Be Necessary, New Research Shows

That skipped breakfast before a morning blood draw may soon be a thing of the past. A large new study suggests that fasting is unnecessary for most routine blood tests, according to PhillyVoice.

The research, published in September in JAMA Internal Medicine, looked at roughly 9.7 million test results from about 101,000 patients. The data came from a hospital in South Korea, where test results were collected between 2021 and 2023.

For decades, patients have been told to avoid eating or drinking anything but water for 8 to 12 hours before bloodwork. The study found that for most of the 121 tests examined, fasting made little to no difference in the results.

Some tests still need an empty stomach. Blood sugar, triglycerides and a pancreatic enzyme called lipase all ran higher in patients who had fasted for less than 8 hours, with blood sugar about 11 percent higher and triglycerides about 20 percent higher. A liver enzyme called gamma-GT was also affected.

Fasting longer than 12 hours offered no extra accuracy. None of the results differed in any meaningful way between people who fasted 8 to 12 hours and those who fasted longer, the researchers found. Skipping both dinner and breakfast adds discomfort without adding precision.

The authors suggest replacing the one-size-fits-all fasting rule with instructions tailored to each test. An accompanying commentary in the journal supported the shift, noting that Denmark and other countries have already moved away from requiring fasting for cholesterol checks.

There are limits to the findings. The study involved patients at a single hospital in South Korea, and the authors say research in more diverse populations is needed before official standards change.

The bottom line for patients: do not change anything on your own. Always follow the fasting instructions from your own doctor or lab, since the tests you are having may be among the handful where fasting still matters.