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Glucose blood test

In short

A typical adult glucose result is 70 to 99 mg/dL (fasting). Food raises glucose for a few hours, so a non-fasting result often sits above this range. When fasting, 100–125 mg/dL (5.6–6.9 mmol/L) is the prediabetes range, and 126 (7.0) or higher the range used for diabetes. Always read your result against the range printed on your own report.

The sugar in your blood, your body's main fuel.

Glucose comes from the food you eat, and insulin, a hormone from the pancreas, moves it into your cells. The typical range here is for a fasting sample, taken after at least 8 hours without food. A sample taken after eating reads higher.

Is my Glucose high or low?

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Typical range

ForRangeUnit
Adults · fasting70–99mg/dL
Adults · fasting3.9–5.5mmol/L

Typical ranges for adults. Labs differ a little, so the range printed next to your result is the one to go by.

If your Glucose is high

Food raises glucose for a few hours, so a non-fasting result often sits above this range. When fasting, 100–125 mg/dL (5.6–6.9 mmol/L) is the prediabetes range, and 126 (7.0) or higher the range used for diabetes.

Common reasons

  • Eating or drinking anything but water before the test
  • Stress, pain or a recent illness
  • Steroid medicines and some other medicines
  • Insulin resistance, when the body responds less to insulin, often with weight gain
  • Prediabetes or diabetes
  • Less often: a pancreas, thyroid or other hormone-gland condition

If your Glucose is low

A slightly low fasting glucose is common and often causes no symptoms. It matters more with shakiness, sweating or confusion, or in people taking diabetes medicines.

Common reasons

  • A long fast before the test
  • A sample left sitting for hours before testing
  • Hard exercise or alcohol in the day before
  • Some diabetes medicines
  • Less often: liver, kidney or hormone-gland conditions
  • Less often: a rare tumor that makes too much insulin

What can throw it off

Food raises glucose, and a sample left sitting for hours before testing can read falsely low.

When it can’t wait

A Glucose of 400 mg/dL or more, or 50 mg/dL or less, usually needs a doctor's attention the same day. Call your doctor’s office, or their after-hours line. If you feel very unwell, call your local emergency number.

Questions to take to your appointment

  1. 1Was this sample fasting, and does that change how you read it?
  2. 2Should this be repeated, or checked with an A1C?
  3. 3Could my medicines or a recent illness explain it?

Read together with

Doctors rarely read Glucose alone. These usually sit next to it.

Quick answers

What is the glucose blood test?

Glucose: The sugar in your blood, your body's main fuel. Glucose comes from the food you eat, and insulin, a hormone from the pancreas, moves it into your cells. The typical range here is for a fasting sample, taken after at least 8 hours without food. A sample taken after eating reads higher.

What is a normal glucose level?

For most adults, glucose is typically 70 to 99 mg/dL (fasting). Some countries print it in mmol/L, so check the unit first. Labs differ a little, so the range printed next to your result is the one to go by.

What does a high glucose mean?

Food raises glucose for a few hours, so a non-fasting result often sits above this range. When fasting, 100–125 mg/dL (5.6–6.9 mmol/L) is the prediabetes range, and 126 (7.0) or higher the range used for diabetes. Common reasons include eating or drinking anything but water before the test; stress, pain or a recent illness; steroid medicines and some other medicines; and insulin resistance, when the body responds less to insulin, often with weight gain. A doctor reads it together with your other results and how you feel.

What does a low glucose mean?

A slightly low fasting glucose is common and often causes no symptoms. It matters more with shakiness, sweating or confusion, or in people taking diabetes medicines. Common reasons include a long fast before the test; a sample left sitting for hours before testing; hard exercise or alcohol in the day before; and some diabetes medicines.

What can affect my glucose result?

Food raises glucose, and a sample left sitting for hours before testing can read falsely low.

When is my glucose result urgent?

A glucose result of 400 mg/dL or more, or 50 mg/dL or less usually needs a doctor's attention the same day. Call your doctor's office or their after-hours line. If you feel very unwell, call your local emergency number.

What should I ask my doctor about my glucose?

Questions worth taking to the appointment: Was this sample fasting, and does that change how you read it? Should this be repeated, or checked with an A1C? Could my medicines or a recent illness explain it?

What this page can’t do

It reads each number on its own.

Doctors read results together — ALT with AST, ferritin with hemoglobin, TSH with free T4. A pattern says more than any single flag.

It doesn't know you.

Your age, your medicines, how you feel and your last result all change what a number means.

It doesn't remember.

Close this page and your results are gone. That's on purpose: nothing was ever sent to us.

We also make Vita: Health Coach, an app for those parts. It reads your whole report with your medicines and history in mind, answers follow-up questions in plain words, and keeps your reports in one place — for you and for the people you look after.

Vita: Health Coach on the App Store

Sources

Stuck on a word? See the medical words. How we choose our sources. More about Vita Health Coach.