There’s no need to fast before every test

Scientists from South Korea conducted the largest retrospective assessment of real data: they studied nearly 10 million test results collected from 670 hospitals across the country. The study included over 100,000 adult patients. To eliminate the influence of individual health characteristics, the experts compared the results for the same individuals at different visits, when the duration of fasting differed. The participants were divided into three groups: those who did not eat for less than 8 hours, between 8 and 12 hours, and for more than 12 hours.

It turned out that the results of the vast majority of tests are practically not affected by the duration of fasting. Of the 121 routine laboratory analyses, only a small fraction showed clinically significant changes. Especially noticeable shifts were recorded if a person had not eaten for less than 8 hours: the glucose level in such cases was about 10.8 percent higher, triglycerides — by 20.1 percent, and lipase, an enzyme of the pancreas, by 36.4 percent at once. At the same time, glucose gradually decreased by about 4.3 mg/dl for each additional hour of fasting.

Prolonging the fast for more than 12 hours did not provide any additional accuracy. For most indicators, there was no difference between the “8-12 hours” and “over 12 hours” groups. The only exceptions were total bilirubin and 25‑hydroxyvitamin D, whose levels were higher during very prolonged fasting.

The widespread requirement to starve can create inconveniences for both patients and laboratories. People have to come in early in the morning on purpose, sometimes even reschedule their visit for another day, and there is an increased workload in clinics at this time. If there is no clear clinical justification for a particular test, such costs may outweigh the benefits.

Based on the data obtained, the researchers propose to abandon the universal rule and switch to individual recommendations: fasting should be mandatory only for those analyses where its effect is really significant. At the same time, it is noted that additional studies involving more diverse populations are needed for the final revision of clinical standards.

Doctors remind you that you should not cancel the preparation for the tests yourself. The decision on the need for fasting and its duration should be made by the attending physician, based on the purpose of the study and the patient’s condition.