A study has found that the common practice of fasting for 8 to 12 hours before a blood test may not be necessary for most test items. Some items, including blood glucose and triglycerides, still require fasting for accurate measurement, it found.

A Korean joint research team including Ulsan University College of Medicine analysed about 10 million blood test results to examine links between fasting time and test values. The findings were published in JAMA Internal Medicine.

The researchers analysed 9,755,547 test results from 101,148 adult patients collected at one 670-bed university hospital in the greater Seoul area from February 2021 to December 2023.

Patients were divided by fasting time of less than 8 hours, 8 to 12 hours, and more than 12 hours, and test values were compared. Among 121 test items that met the analysis criteria, 27 showed differences beyond the allowable margin of error. When results from the same patient were compared, such differences were confirmed in only 10 items.

In particular, in cases of fasting for less than 8 hours, glucose was 10.8 percent higher, triglycerides 20.1 percent higher and lipase, a pancreatic digestive enzyme, 36.4 percent higher.

By contrast, blood cell counts, kidney function indicators, electrolytes and most liver enzymes showed little difference by fasting time. In same-person comparisons of analysable items, no differences beyond the allowable margin of error were found between the group fasting 8 to 12 hours and the group fasting more than 12 hours.

The researchers suggested setting fasting times by test item rather than applying a single fasting standard to all blood tests.

The study was an observational analysis of past clinical data from a single hospital, and it does not mean fasting can be omitted for all tests. The researchers said further verification is needed. Patients scheduled for blood tests should not skip fasting on their own and should follow medical staff guidance.