Fasting blood sugar levels and test info

The normal range of fasting blood sugar is anything less than 100 mg/dL. Learn how to prepare for a fasting blood sugar test and how to lower your levels.

By Karen Berger, Pharm.D. | Updated on Jun. 30, 2023

Blood sugar (or blood glucose) is the main sugar in your blood. Blood sugar comes from the foods you eat. The blood carries glucose to the cells in your body to be used for energy.

In order to determine the amount of glucose in your blood—your doctor may order a fasting blood sugar test. A fasting blood sugar test is done in the morning when you have not had anything to eat or drink (except water) for at least eight to 12 hours. The fasting blood sugar result can be used to diagnose prediabetes or diabetes. What do these test results mean? According to the American Diabetes Association:

A fasting blood sugar of 99 mg/dL or less is normal
A fasting blood sugar of 100-125 mg/dL indicates prediabetes
A fasting blood sugar of 126 mg/dL or more indicates diabetes

Most healthcare providers will take a sample of your blood and repeat the test on at least one other occasion to confirm a diagnosis unless you have symptoms and/or your blood sugar is very high.

Fasting blood sugar test

A fasting blood sugar test measures your blood sugar when you are in a fasting state. It is usually done in the morning after you have been fasting (not eating) for at least eight to 12 hours. Depending on your age, family history, medical conditions, and risk factors, your doctor will decide how often you should have a fasting blood sugar test.

How to prepare

There is not much to do to prepare for a fasting blood sugar test in the lab. All you have to do is go to the lab with your blood test orders. It’s best to go in the morning after you have not had anything to eat or drink (except water) for at least eight to 12 hours. The phlebotomist will take a blood sample, and depending on the lab, you should have results in anywhere from 24 to 72 hours. Having a fasting blood sugar test is just like any other blood work—in fact, it’s often done in combination with other blood work that your doctor orders.

Can I do a fasting blood sugar test at home?

If you want to do a fasting blood glucose test at home, you can use a blood glucose meter to perform the test yourself. You may need to watch the training videos if you have not used a meter before. You can use the blood glucose meter to check your fasting blood sugar. If you are interested in a more complete picture of your blood sugar, you can ask your healthcare professional if continuous glucose monitoring is an option for you. Continuous glucose monitors (CGMs) use a sensor to capture blood sugar data frequently throughout the course of a day—every one to five minutes, depending on the particular CGM. Using a CGM, you would be able to see your fasting blood sugar every day, as well as throughout the day and night.

Other tests to diagnose diabetes

Hemoglobin A1C: Your doctor may also order a test called hemoglobin A1C. This test measures your blood glucose control over a period of about three months. An A1C test does not require fasting. However, your doctor may order the A1C test with other blood work that does require you to be fasting, so it is fine to get the A1C test when you are fasting.

An A1C of less than 5.7% is normal
An A1C of 5.7 to 6.4% indicates prediabetes
An A1C of 6.5% or more indicates diabetes

Oral glucose tolerance test (OGTT): This test will check your blood sugar before and 2 hours after you drink a sugary drink. It gives your doctor a picture of how your body processes sugar. At the two-hour mark,

A blood sugar of 200 mg/dL or more indicates diabetes
A blood sugar of 140-199 mg/dL indicates prediabetes
A blood sugar of less than 140 mg/dL is a normal result

Random plasma glucose test: This is also called a casual plasma glucose test and can be done at any time of the day when you have severe diabetes symptoms. A blood sugar of 200 mg/dL or more indicates diabetes.

You can consult your healthcare professional about what kind of testing—and how often— you need to check your blood glucose levels.

Normal fasting blood sugar levels

The normal range of fasting blood sugar is anything less than 100 mg/dL. This level applies to adults and children without diabetes. A higher number may require further testing or treatment. Consult your healthcare provider to interpret your numbers and what they mean.

Normal fasting blood sugar levels by age
Age	< 6 years old	6-12 years old	13-19 years old	20+ years old
With diabetes	80-180 mg/dL	80-180 mg/dL	70-150 mg/dL	80-130 mg/dL
Without diabetes	Less than 100 mg/dL	Less than 100 mg/dL	Less than 100 mg/dL	Less than 100 mg/dL

Fasting blood sugar levels chart for adults
Demographic	Risk	Fasting blood sugar in mg/dL	Action needed
Adults with diabetes	Dangerously high	A dangerously high number will vary, depending on your target ranges and treatment plan. Your healthcare professional will give you more information.	Check ketones if required/Seek emergency medical care as outlined on your treatment plan
	High	>130 mg/dL, or possibly higher, depending on your target range	Follow the treatment plan provided by your healthcare professional
	Normal	70-130 mg/dL depending on your target range	Follow your treatment plan provided by your healthcare professional
	Low	<70 mg/dL depending on your target range	Follow your treatment plan provided by your healthcare professional
	Dangerously low	<54 mg/dL but may vary depending on your range	Emergency intervention with glucagon and emergency medical care may be required depending on the patient’s status. Patients who are able to eat should consume fast-acting carbs as detailed in their treatment plan.
Adults without diabetes	High	A fasting blood sugar of 100-125 mg/dL is considered high, and in the prediabetes range A fasting blood sugar of 126 mg/dL or more is considered high and in the diabetes range	Consult your healthcare provider. Adults with prediabetes may be able to lower blood sugar with lifestyle changes such as a healthy diet and exercise (and possibly medication). Adults with diabetes generally will need medication, diet, and exercise, and some patients will need insulin.
	Normal	70-100 mg/dL	Consult your healthcare provider- generally, no action is required.
	Low	<70 mg/dL	Consult your healthcare provider

Impaired fasting glucose test result

100-125 mg/dL: Prediabetes

If your fasting blood sugar is between 100-125 mg/dL, this means you have prediabetes. Prediabetes means that your blood sugar is higher than normal but not high enough to be diagnosed with Type 2 diabetes. More than 1 in 3 American adults has prediabetes, and of those, more than 80% do not know they have it. Prediabetes increases your risk for Type 2 diabetes and other complications like heart attack and stroke. If your doctor tells you that you have prediabetes, they may recommend lifestyle changes including dietary changes and an exercise program. Some healthcare professionals prescribe medication for prediabetes.

126+ mg/dL: Diabetes

If your blood sugar is 126 mg/dL or more, this means you have diabetes. Your doctor may repeat the test to confirm the diagnosis. If you have diabetes, your doctor will start you on medication (there are both oral and injectable medications) and a healthy diet and exercise program. Some adults with Type 2 diabetes will also require insulin injections.

High blood sugar in the morning

Some patients will find that they have high fasting blood sugar, but then blood sugars return to normal levels during the day. What is the reason for this? Stephanie Redmond, PharmD, CDCES, BC-ADM, is the founder and VP of drstephanies.com. She offers several explanations—and also recommends wearing a CGM to help you identify how and why your numbers fluctuate. Some people experience the dawn phenomenon, Dr. Redmond explains. “This is when the liver may be overproducing and releasing extra sugar into the bloodstream, which indicates insulin resistance and fatty liver disease.”

Another cause of early morning high blood sugar can be the Somogyi Effect. “If you are on insulin or certain blood sugar medication like glipizide, glimepiride, or glyburide, your sugars can fall too low in the middle of the night, leading to a rebound high sugar,” Dr. Redmond explains.

Dr. Redmond also points out that snacking at bedtime or in the middle of the night can increase morning blood sugars. While having a healthy snack (that includes protein) a few hours before bedtime can help stabilize blood sugars, it’s best for most people not to eat for at least two hours before bed, she says.

Symptoms of an imbalance

If your blood sugar becomes low (hypoglycemia) or high (hyperglycemia), you may start to feel symptoms. Depending on your diagnosis, your doctor may give you a target range for your blood sugar and tell you what to do if your blood sugar becomes too low or too high. People who do not have diabetes or prediabetes generally will not need to worry about low or high blood sugar symptoms.

Everyone has different symptoms of low blood sugar. Symptoms of low blood sugar may include:

Feeling shaky, nervous, irritable, or anxious
Feeling dizzy, lightheaded, sleepy, or weak
Hunger
Nausea
Sweating
Chills
Confusion
Fast heartbeat
Pale skin
Blurry vision
Headaches
Numbness and tingling
Incoordination
Seizures

You will need to treat low blood sugar because if your sugar continues to drop, the brain stops working properly and this can lead to confusion, slurred speech, and drowsiness. If blood sugar stays low for too long, it may lead to seizures or coma (and very rarely can cause death). If you are at high risk for having low blood sugar levels, it is important to carry a source of fast-acting carbohydrates with you at all times, such as glucose tablets or Smarties, to treat low blood sugar quickly. Your doctor may also prescribe Baqsimi, which is a nasal spray that contains glucagon. Baqsimi can be used by family members or caregivers to treat a low blood sugar emergency if you are unable to eat. All of this information on how to treat low blood sugar will be in your treatment plan.

If your blood sugar becomes too high, this is called hyperglycemia. If you have high blood sugar, you may become very thirsty and need to urinate frequently.

If you do not treat high blood sugar, a condition called diabetic ketoacidosis (DKA) may occur. DKA is life-threatening and requires emergency treatment. Your doctor will tell you when you need to test for ketones, generally, if your blood sugar is 240 mg/dL or more. Symptoms of DKA include:

Fruity-smelling breath
Shortness of breath
Dry mouth
Nausea and vomiting

People with diabetes, especially those who inject insulin, should wear medical identification at all times that states they have diabetes. This alerts first responders to the condition in the event of an emergency.

How to lower fasting blood sugar

There are a number of options you can try to lower fasting blood sugar. Even making small changes can make a significant impact on lowering blood sugar over time.

Dietary changes: You may want to consult a registered dietician specializing in prediabetes and diabetes. A dietician can help you plan balanced meals and snacks. The goal is not to avoid all carbohydrates but to limit certain carbohydrates such as cookies and pastries, while incorporating proteins and healthy carbs (with fiber), such as fruits, vegetables, and whole grains, into your diet.
Exercise regimen: Consult your doctor about an appropriate regimen that increases physical activity and considers your medical conditions. The National Institute of Health recommends 150 minutes of moderate-intensity activity per week, which can be done by walking for 30 minutes a day, five days per week—and adding strength training at least twice weekly.
Lose excess weight, if needed: Studies show that losing a small amount of weight can lead to big changes. People who lose 5% to 10% of body weight can see a dramatic improvement in blood sugar levels, as well as other medical conditions. For a person who is 200 lbs, a 5% weight loss would be 10 pounds, and a 10% weight loss would be 20 pounds.
Drink plenty of water: Studies show that drinking plenty of water can reduce the risk of diabetes.
Lower stress: Stress can lead to changes that contribute to the development of Type 2 diabetes. Focus on ways to lower stress, such as therapy, relaxation, meditation, yoga, or other relaxing activities.
Get enough (high-quality) sleep: Try to get 7 or 8 hours of sleep every night. Not getting enough sleep can affect your blood sugar and make you hungrier the next day.
Wear a continuous glucose monitor (CGM): CGMs are more affordable—and portable—than finger sticking. Wearing a CGM offers immediate insight into how food, exercise, and other factors affect your blood sugar. Many people find that wearing a CGM provides a lot of motivation to improve their lifestyle because they see immediate results. If you do not want to wear a CGM, talk to your healthcare professional about monitoring your blood sugar with a blood glucose meter.
Medication: Your healthcare professional will determine if you need medication.
Dietary supplements: Dr. Redmond suggests patients discuss certain dietary supplements with their healthcare professional to see if they would be appropriate, such as berberine, cinnamon, and/or chromium.

What is the best way for pregnant women with gestational diabetes to lower their blood sugar? “Everyone is unique with regard to blood sugar response, so the best approach is to try different methods and monitor blood sugars regularly to see what works best for you,” says Dr. Redmond. “However, I would consider focusing on good sleep hygiene as poor sleep quality will inevitably increase blood sugar.”

“Some people benefit from having a small protein-based snack a few hours before bedtime to see if it helps,” says Dr. Redmon. This is because protein is more slowly converted to sugar by the body. “If the liver senses a slow steady influx of glucose throughout the night, this gives it the message via hormone signaling not to make any more glucose.”

Patients with gestational diabetes may also need medication and/or insulin and should consult their healthcare professional for medical advice.

Many patients ask about the best ways to lower blood sugar instantly. “I am not aware of any,” says Dr. Redmond. “Truly, any food will either have a negligible effect or may increase blood sugar. Eating more fiber and non-starchy vegetables over time will help stabilize blood sugar, but they will not decrease blood sugar instantly.”

How to prevent Type 2 diabetes

If you are diagnosed with prediabetes, you can follow many of the tips above in the section “How to lower fasting blood sugar.” You can consult with your healthcare professional and determine which methods may be most effective and attainable for you. The Centers for Disease Control and Prevention (CDC) offers a National Diabetes Prevention Program (National DPP) lifestyle change program. This program helps patients make changes that may prevent or delay Type 2 diabetes.

When to contact a doctor about glucose numbers

Having diabetes can be very overwhelming, especially at the beginning. You can work closely with your healthcare professional and ask about consulting with a Certified Diabetes Care and Education Specialist (CDCES) and/or a registered dietician.

Based on your numbers, your doctor will tell you how often and when to check your blood sugar at home. You can talk with your doctor about the best way to do this—by using a blood glucose meter or a CGM. Your doctor will give you a treatment plan that details your target blood sugar range and what to
do if your blood sugar gets too low or too high. You should always consult your doctor if you have any questions or concerns.

In some cases, you may need emergency medical attention. If you have low blood sugar that causes you to become unconscious or have seizures, your family members or caregivers should call 911, and an ambulance can take you to the emergency room. If your blood sugar is high and you test positive for ketones, you will also need emergency medical attention.

The American College of Emergency Physicians states, “Anyone who thinks they’re having a medical emergency should not hesitate to seek care. Federal law ensures that anyone who comes to the emergency department is treated and stabilized and that their insurance provides coverage based on symptoms, not a final diagnosis.” If you are unsure if you need emergency medical attention, it is better to be safe and seek emergency care.