Blood glucose levels vary, depending on a person’s health status and whether they have eaten. People without diabetes typically have between 72–140 milligrams of glucose per 1 deciliter of blood.

People who have diabetes tend to have slightly higher blood glucose, or sugar, levels at around 80–180 milligrams per deciliter (mg/dL).

The Centers for Disease Control and Prevention (CDC) recommend that monitoring blood glucose levels helps people stay within their target ranges. Keeping in a healthy range can prevent long-term complications of diabetes, such as vision loss, heart disease, and kidney disease.

In this article, we discuss normal ranges for blood sugar levels. We also cover how and why doctors test blood sugar levels.

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A glucose monitor can help a person measure blood glucose levels.

Blood sugar levels change throughout the day. Typically, blood sugar levels are at their lowest first thing in the morning or after a period of fasting. Blood sugar levels increase during and after meals, as the body digests food.

The following chart outlines normal blood sugar ranges for people with and without diabetes, depending on the time of day:

Time of dayTarget blood sugar for people without diabetesTarget blood sugar for people with diabetes
Before meals or while fasting72–99 mg/dL80–130 mg/dL
2 hours after the start of a mealless than 140 mg/dLless than 180 mg/dL
A1C results: Average over a 3-month periodless than 5.7%less than 7%

Abnormal blood sugar levels

Abnormal blood sugar levels occur when there is either too much or little sugar in the blood. The blood sugar ranges for each are:

What is a blood glucose test?

There are two ways to measure blood glucose levels:

  • Blood sugar test. This measures the current level of glucose in the blood.
  • A1C test. This measures the average blood glucose level over the past 2–3 months. This test occurs in a laboratory.

People can measure their blood sugar levels with either a blood sugar meter or a continuous glucose monitor.

A continuous glucose monitor uses a sensor to measure blood sugar levels. A doctor inserts the sensor under the skin, usually in the abdomen or arm. The sensor transmits information to a monitor that displays glucose levels every few minutes.

A blood sugar meter measures the amount of glucose in a drop of blood, usually from the finger.

Follow these steps when using a blood sugar meter:

  1. Thoroughly wash the hands and disinfect the meter.
  2. Gather the meter, a test strip, a lancet, and an alcohol wipe.
  3. Rub the hands together to encourage blood flow to the fingertips.
  4. Turn the meter on and insert the test strip.
  5. Wipe the fingertip with the alcohol pad and let the alcohol evaporate.
  6. Prick the finger with the lancet.
  7. Gently squeeze at the base of the finger until a drop of blood forms on the fingertip.
  8. Place the blood droplet on the test strip.
  9. Wait for the meter to display the blood sugar measurement.
  10. Record the results, adding notes about anything that may have contributed to an abnormal reading, such as food or physical activity.
  11. Properly dispose of the wipe, lancet, and test strip.

The A1C test measures the percentage of glucose bound hemoglobin in a person’s blood.

According to The National Institutes of Health (NIH), this gives a general picture of a person’s blood glucose levels over the past 2–3 months.

Abnormal A1C test results do not necessarily mean a person has diabetes. A doctor will confirm these findings with another blood glucose test.

The doctor may recommend running more tests, such as blood work, to rule out other conditions that can affect blood sugar levels.

When should a person get a A1C blood sugar test?

The CDC recommend that people with diabetes get an A1C test at least twice a year.

Doctors use A1C results to monitor how well a person responds to a certain glucose management regime. They can also use A1C tests to diagnose prediabetes and diabetes.

Symptoms of diabetes that may prompt an A1C test

As mentioned by the NIH, a doctor may recommend an A1C test if a person shows signs of poor glucose control, diabetes, or prediabetes.

Warning signs can include:

  • increased thirst
  • increased urination, especially at night
  • increased hunger
  • extreme fatigue
  • recurring infections
  • numbness or tingling in the hands or feet
  • slow healing sores
  • blurry vision

Doctors may also recommend an A1C test for people who have the following risk factors for prediabetes:

What happens during the test?

Most people can take an A1C test at any time without preparing beforehand. However, a doctor may sometimes request that a person avoids eating or drinking for 8 hours before the test.

Women who are pregnant may need to drink a sugary beverage 1 hour before the test.

A doctor or nurse will collect a blood sample, usually from a vein in the arm or hand. They will send the sample to a laboratory for analysis.

Risks of the test

A1C tests are safe and reliable methods of measuring a person’s blood sugar levels. These tests carry a low risk of complications.

However, people may experience temporary pain or bruising at the injection site. Using an unclean needle or lancet can lead to an infection.

A doctor can make dietary and lifestyle recommendations that address an individual’s needs. Doctors can also prescribe insulin and other medication that help stabilize blood sugar levels.

People can use the following tips to keep their blood glucose within a healthy range:

  • closely monitor blood sugar levels
  • maintain a healthy weight
  • exercise regularly
  • eat foods with a low glycemic index
  • increase dietary fiber intake
  • drink plenty of water
  • eat regular times and do not skip meals

Learn more about low-glycemic foods here.

People can lower high blood sugar by:

  • restricting carbohydrate intake
  • choosing complex carbs over simple carbs
  • eating more whole grains, nonstarchy vegetables, and fruit
  • controlling portion size
  • exercising regularly
  • getting plenty of sleep
  • staying hydrated

People can raise low blood sugar by:

  • consuming 15 grams of fast acting carbs, such as glucose tablets or 4 ounces of juice
  • eating dried fruit or applesauce
  • eating 1 tablespoon of peanut butter
  • using a glucose injection as a doctor prescribes

Type 1 and type 2 diabetes can affect how the body produces and responds to insulin. When insulin is only available in smaller quantities, or cells no longer respond to it, sugar does not enter these cells and remains in the blood.

Type 1 diabetes: The beta cells that make insulin in the pancreas are damaged or destroyed, so sugar stays in the blood for longer.

Type 2 diabetes: The cells in the liver, muscles, and fat tissue no longer respond to insulin, and they release more sugar into the blood. The beta cells not producing enough insulin compounds in this situation.

People who have diabetes can experience high blood sugar levels, or hyperglycemia, because the cells in their body cannot absorb sugar from the blood.

Factors that can raise a person’s blood sugar level include:

  • taking too little insulin
  • eating too many carbs
  • stress
  • lack of physical activity
  • certain medications
  • steroids

If people take too much insulin, exercise more than usual, or skip a meal, they may experience low blood sugar levels, or hypoglycemia.

People can have abnormal blood sugar levels without having diabetes.

Causes of hypoglycemia without diabetes include:

  • drinking too much alcohol
  • taking certain medications
  • eating insufficient food
  • adrenal or pituitary gland disorders
  • kidney or pancreas problems

Regularly monitoring blood sugar levels is a vital aspect of diabetes treatment. A person’s diet, level of physical activity, and family history can impact their blood sugar levels.

High or low blood sugar can lead to symptoms, such as fatigue, dizziness, and vision problems.

Uncontrolled blood sugar levels can lead to long-term health conditions, including vision loss, heart disease, and kidney disease.