You may have to fast—avoiding anything but water—for eight to 12 hours before a blood test. This is because nutrients from foods and beverages are absorbed into your blood, which can cause inaccurate results.
Make sure you are clear about whether or not you need to fast for the test(s) you are scheduled for so you can avoid having to repeat them.
Continued: https://www.verywellhealth.com/fasting-for-blood-work-5217491
