Guide

Most cortisol blood tests don’t require fasting, but test timing and certain meds or supplements can change results.

Most cortisol tests don’t require fasting, yet timing, meds, and your lab’s instructions can change what you should do the night before.

Most cortisol blood draws don’t require fasting, yet the clock time, recent activity, and certain supplements can shift results more than breakfast.

Most people don’t need fasting for a creatinine blood test, but some lab panels that include creatinine do require an overnight fast.

Some diabetes blood tests require an 8+ hour fast, while A1C and random glucose usually don’t—your lab order decides what “fasting” means.

Some CT exams need a short fast, while many don’t; the rule hinges on contrast use, the body area, and the imaging center’s prep sheet.

Most people don’t fast for the 1-hour screening drink, but the longer tolerance test usually needs an 8-hour fast.

Most urine drug tests don’t require fasting; eat as usual unless your test order spells out food rules for that visit.

No, most heart ultrasounds let you eat and drink normally, but a few types (like a probe-down-the-throat test or some stress tests) may ask for fasting.

A ferritin test alone usually doesn’t require fasting; fast only when your order includes iron studies or other fasting labs.