Blood glucose after fasting: used in diabetes and prediabetes assessment.
What it is
Fasting plasma glucose in mmol/L. Timing of the last meal matters; follow the lab’s fasting instructions (usually 8 to 12 hours, water allowed).
Fasting plasma glucose is taken after an overnight fast (water allowed). Clinicians use it with history and other tests when assessing glucose control; this guide cannot diagnose you.
Why it matters
Laboratories report fasting glucose against their own reference intervals. UK clinical guidelines use defined cut-offs when assessing diabetes risk; only a qualified clinician can interpret your result in that context. Confirm unexpected results and never change diabetes treatment from a single reading without advice.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Glucose fuels the brain and working muscle. Insulin and counter-regulatory hormones keep fasting levels in a narrow band; insulin resistance raises fasting glucose over time.
The brain needs a steady glucose supply; muscle uses glucose heavily in intense work. Insulin-mediated uptake into tissues keeps fasting levels controlled; resistance raises fasting glucose over years.
For athletes
Dawn phenomena and hard evening sessions can affect morning glucose. Athletes with type 1 diabetes need individualised plans, this encyclopaedia entry is not insulin advice.
Hard late sessions and glycogen depletion can affect morning glucose. Athletes with diabetes need individualised plans with their diabetes team, this page is not insulin dosing advice.
