Impaired Fasting Glucose (IFG)

Impaired fasting glucose, or IFG, is one of the ways prediabetes shows up on a blood test. It describes a fasting glucose that is higher than normal but below the diabetes threshold. Understanding what IFG measures — and how it differs from the related term impaired glucose tolerance — helps make sense of a result and the conversation that should follow with a clinician.

What IFG means

IFG is defined by the level of glucose in your blood after an overnight fast, measured as fasting plasma glucose (FPG). According to the American Diabetes Association (ADA), the categories are:

• Below 100 mg/dL — normal fasting glucose.
• 100–125 mg/dL — impaired fasting glucose (IFG), a form of prediabetes.
• 126 mg/dL or higher — in the diabetes range (confirmed on repeat testing).

So IFG is the band between clearly normal and the diabetes cutoff, measured specifically in the fasting state. It is one of three standard ways prediabetes is identified, alongside the A1c test and the oral glucose tolerance test. For the full picture, see the prediabetes guide and our overview of what prediabetes is.

How IFG differs from IGT

IFG is easy to confuse with impaired glucose tolerance (IGT), but they measure different things. IFG uses a single fasting blood sample and reflects the baseline glucose your body maintains overnight. IGT, by contrast, is based on the 2-hour value of an oral glucose tolerance test (OGTT) — 140–199 mg/dL per the ADA — which reflects how efficiently your body clears a measured glucose drink. Because they capture different aspects of glucose handling, the two can disagree: some people have IFG but normal glucose tolerance, some have IGT with normal fasting glucose, and some have both. Our article on impaired glucose tolerance covers the post-challenge side in detail.

What IFG means for risk

IFG is a recognised marker that metabolic risk is elevated. It is frequently associated with insulin resistance and with a higher likelihood of developing type 2 diabetes over time compared with people who have normal fasting glucose. That said, IFG is a category of prediabetes, not diabetes, and the NIDDK and CDC emphasize that prediabetes is often modifiable. Being in this range is best understood as an early signal and an opportunity, rather than an inevitability.

How IFG is found

IFG usually turns up on a routine fasting blood test, often ordered as part of a general check-up or because a person has risk factors for diabetes. Because prediabetes is frequently silent, IFG is typically detected by testing rather than by symptoms — see prediabetes symptoms for why the absence of symptoms is not reassuring on its own. Since glucose can vary from day to day, a single reading is a starting point; clinicians generally confirm with repeat or additional testing, as described in how prediabetes is diagnosed.

Next steps

If a fasting result falls in the IFG range, the sensible next step is a conversation with a clinician who can interpret it alongside your A1c, medical history, and risk profile, and arrange any confirmatory testing. From there, discussion often turns to lifestyle steps — eating patterns, physical activity, sleep, and weight — that public-health programs describe as reducing the risk of progression to type 2 diabetes. Some people also use continuous glucose monitoring under professional guidance for added day-to-day context. Endobits is clinical decision-support software used under clinician oversight; it helps put results like IFG in context, but it does not diagnose or treat.

Sources

American Diabetes Association — Understanding Diagnosis (fasting plasma glucose criteria). Centers for Disease Control and Prevention — Prediabetes — Your Chance to Prevent Type 2 Diabetes. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) — Diabetes Tests & Diagnosis.

Related: The prediabetes guide · Impaired glucose tolerance · How prediabetes is diagnosed · Glossary