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Biomarker library / Metabolic

Fasting plasma glucose (FPG)

Also called fasting blood sugar, fasting blood glucose

The glucose concentration in your blood after at least 8 hours without calories. It is a snapshot of how your body holds glucose in the fasted state, driven mostly by the liver's overnight glucose output and how well insulin restrains it.

Written by the VitalDecades editorial team Reviewed by the editorial review process Updated

01  /  Reference ranges

What counts as normal

Scale in mg/dL. Cut points from the sources listed below.
Population Nonpregnant adults, fasting
Category Normal (below the prediabetes range)
Range under 100 mg/dL ADA's diagnosis page states normal as less than 100 mg/dL.
Source Standards of Care in Diabetes 2026, Section 2: Diagnosis and Classification of Diabetes (ADA)

Effective

Population Nonpregnant adults, fasting
Category Prediabetes (impaired fasting glucose)
Range 100 to 125 mg/dL
Source Standards of Care in Diabetes 2026, Section 2: Diagnosis and Classification of Diabetes (ADA)

Effective

Population Nonpregnant adults, fasting
Category Diabetes
Range 126 or higher mg/dL Fasting is at least 8 hours without calories.
Source Standards of Care in Diabetes 2026, Section 2: Diagnosis and Classification of Diabetes (ADA)

Effective

Population Nonpregnant adults, 2-hour OGTT (75 g)
Category Prediabetes (impaired glucose tolerance)
Range 140 to 199 mg/dL
Source Standards of Care in Diabetes 2026, Section 2: Diagnosis and Classification of Diabetes (ADA)

Effective

Population Nonpregnant adults, 2-hour OGTT (75 g)
Category Diabetes
Range 200 or higher mg/dL
Source Standards of Care in Diabetes 2026, Section 2: Diagnosis and Classification of Diabetes (ADA)

Effective

Normal vs optimal

The ADA's public diagnosis page states normal fasting glucose as less than 100 mg/dL and normal 2-hour OGTT glucose as less than 140 mg/dL. The Standards themselves define the abnormal ranges and treat everything below them as normal. There is no separately published "optimal" cutoff, and we do not invent one.

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02  /  Why it matters

What the number tells you

Fasting glucose is a diagnostic criterion for diabetes (126 mg/dL or higher) and defines impaired fasting glucose, one form of prediabetes (100 to 125 mg/dL), under the ADA Standards of Care 2026. It moves faster than A1C, so it can show a change within weeks. The 2-hour value on a 75 g oral glucose tolerance test is the companion measure: 140 to 199 mg/dL is impaired glucose tolerance, 200 or higher is diabetes.

03  /  In practice

Testing and what moves it

When it is tested

  • As part of a basic or comprehensive metabolic panel at a routine visit.
  • USPSTF screening for adults 35 to 70 with overweight or obesity, about every 3 years if normal.
  • Fasting is defined as no caloric intake for at least 8 hours; water is fine.

What raises it

  • Insulin resistance and reduced insulin secretion.
  • Acute illness, steroids and some other medications, poor sleep the night before, and a short fast (under 8 hours).

What lowers it

  • Weight loss, activity, and glucose-lowering medication.
  • Prolonged fasting or heavy exercise the day before can push it lower; alcohol the previous evening can lower it in some people.

04  /  Related

Read next

Hemoglobin A1C A1CTriglycerides TG

Frequently asked questions

Which is better, fasting glucose or A1C? ▼

The ADA accepts either for diagnosis. Fasting glucose is a snapshot that responds quickly; A1C averages about three months and needs no fasting. Clinicians often use both, and a diagnosis usually needs a repeat or a second abnormal test.

What does 100 to 125 mg/dL mean? ▼

Under the ADA Standards of Care 2026 that range is impaired fasting glucose, a form of prediabetes. It is a signal to act on weight, activity and diet, and to retest.