Guide

Most thyroid blood tests don’t need fasting, but combo lab orders and a few prep slip-ups can skew results or force a redraw.

Most urine drug screens don’t need fasting; eat as usual and skip overdoing fluids so the sample doesn’t end up too diluted.

No, fasting isn’t required for an A1C blood test, so you can eat and drink as you normally would unless your clinician ordered other fasting labs.

No, an A1C blood test doesn’t need fasting unless you’re also getting labs like fasting glucose or lipids.

Most heart ultrasounds don’t require fasting; you’ll fast for a transesophageal echo and sometimes before a stress echo.

Most standard chest ultrasounds let you eat and drink normally, while throat-based or exercise versions often require a short fast.

Fasting before a CT scan depends on the body area and contrast use; many non-contrast scans need no fasting, while contrast scans often need a short no-food

No—most people should eat a normal meal before donating, since an empty stomach can raise the odds of dizziness.

Most people don’t fast for the 1-hour drink test, but the 3-hour test often needs an 8-hour fast, so the rule depends on which test you’re taking.

An empty stomach is usually required: stop food 6 hours before anesthesia and stop clear drinks 2 hours before, unless told otherwise.