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Lab test
What is a fasting glucose test, and what are normal fasting blood sugar levels?
A fasting glucose test measures blood sugar after not eating, usually overnight, to screen for prediabetes and diabetes. NIDDK, citing the American Diabetes Association, lists 99 mg/dL or below as normal, 100 to 125 mg/dL as prediabetes and 126 mg/dL or above as diabetes. A diagnosis is usually confirmed with a second test.
What does the fasting glucose test measure?
A blood glucose test measures the sugar in your blood, the body’s main source of energy. Insulin helps move glucose from the blood into cells. MedlinePlus
A fasting plasma glucose (FPG) is drawn after a period without food, so it is not affected by a recent meal. MedlinePlus
Why is the fasting glucose test ordered?
- As part of a routine checkup, often inside a basic or comprehensive metabolic panel. MedlinePlus
- To screen for prediabetes and diabetes; MedlinePlus notes the American Diabetes Association recommends screening from age 35. MedlinePlus
- To look into symptoms of high or low blood glucose, or to monitor medicines that may affect it. MedlinePlus
What are typical fasting glucose ranges?
NIDDK lists the American Diabetes Association categories for people who are not pregnant. NIDDK
Reference ranges differ between laboratories and testing methods, and many also differ by age, sex, pregnancy or the phase of the menstrual cycle. The range printed on your own report is the one that applies to your result, and a clinician interprets it alongside your history.
| Category | Fasting plasma glucose |
|---|---|
| Normal | 99 mg/dL or below |
| Prediabetes | 100 to 125 mg/dL |
| Diabetes | 126 mg/dL or above |
ARUP Laboratories publishes its glucose reference interval "by report", because it can vary with the instrument used. ARUP Laboratories
What can affect fasting glucose results?
- Eating before the draw changes the result, which is why the test is done after fasting. MedlinePlus
- Certain medicines and conditions affecting the pancreas or adrenal glands can raise blood glucose. MedlinePlus
- Pregnancy uses different cutoffs. NIDDK
When should you talk to a clinician about a fasting glucose result?
- Usually a second test confirms diabetes; ask the clinician who ordered it what a result outside the normal category means for you. NIDDK
DiscoverMedica explains what a test measures and what named sources publish. It does not interpret individual results; the clinician who ordered your test, or one you choose, does.
Where can you get a fasting glucose test?
A clinician can order it as part of routine or follow-up care. Some services also let you order lab tests yourself; check that a service’s panel includes this marker, which laboratory runs it, and who reviews the result with you.
- Function HealthAnnual membership for broad lab panels, drawn at Quest sites or at home.
- Quest HealthOrder individual lab tests from Quest Diagnostics online, without a doctor’s visit.
Fasting Glucose Test: questions, answered
What is a normal fasting blood sugar?
NIDDK, citing the American Diabetes Association, lists a fasting plasma glucose of 99 mg/dL or below as normal, 100 to 125 mg/dL as prediabetes and 126 mg/dL or above as diabetes, for people who are not pregnant. A diagnosis usually needs a second test to confirm it.
How long do I need to fast before a glucose test?
Follow the instructions from whoever orders the test. A fasting glucose is typically drawn after an overnight fast, and when it is part of a metabolic panel MedlinePlus notes you may need to fast for several hours or longer. MedlinePlus lists certain medicines among the causes of higher blood glucose, so mention what you take.
Is fasting glucose the same as A1C?
No. Fasting glucose is a snapshot of blood sugar at one moment after fasting, while A1C reflects average blood sugar over about three months. NIDDK lists separate diagnostic cutoffs for each, and clinicians often use both. NIDDK notes that a second test is usually used to confirm a diagnosis.
Sources
- MedlinePlus: Blood Glucose Test
- NIDDK: Diabetes Tests and Diagnosis
- ARUP Laboratories: Glucose, Plasma or Serum (test 0020024)
Last reviewed October 7, 2026. Every source above was checked on or before that date. Educational information only, not medical advice; it does not replace a conversation with a licensed clinician. DiscoverMedica does not employ clinicians.
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