Fasting blood glucose
Your glucose after 8 to 12 hours without food, water only: a common baseline measure.
Fasting glucose is measured first thing, before food, after 8 to 12 hours without calories: water only, since coffee, juice, and even gum count as breaking the fast. It reflects the glucose your liver releases overnight and is a standard screening number. Fasting much longer than 12 hours can actually raise the reading, as the liver starts releasing stored glucose to keep you fueled.
Common reference points: under 100 mg/dL (5.6 mmol/L) is typical, 100–125 suggests prediabetes, and 126 or above on repeat testing is in the diabetes range.