Everything You Need to Know About Blood Sugar Tests

Diabetes is a chronic condition that you are either born with or develop over time that affects the way your body processes the food you eat. Nearly 35 million Americans have some form of diabetes. This condition can lead to a number of serious complications.

There is no cure for diabetes, but careful management of the condition can help you avoid serious problems.

Everything we eat is broken down to simple components that our cells can use. For energy, our bodies use glucose—a simple sugar. This glucose flows through your body in your bloodstream until it reaches cells that need energy. But glucose can only enter these cells with a type of key, and this key is a hormone called insulin.

There are different conditions that affect how your body makes and uses insulin, and how well glucose can get into your cells to give your body the energy you need. These conditions include the three main types of diabetes—type 1, type 2, and gestational diabetes.

No matter what type of diabetes you have, the most important part of managing the disease is monitoring your blood glucose and taking the necessary steps when these levels get too low or too high.

This article will review how blood glucose—sometimes called blood sugar—is measured, how and when you can test it, and what the results mean.

blood sugar testing

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Blood Sugar and Diabetes

Blood sugar, or blood glucose, is the main type of sugar in your body. This is different from the sugar that you eat in foods. Everything you eat or drink is broken down into basic pieces as you digest them. Glucose is the most basic form of the food you eat, and it's the main form of energy your body uses.

For your body to work well, every cell needs a regular supply of glucose to function. They also need a chemical called insulin that moves this glucose from your bloodstream into the cells that need it. Without insulin, glucose will keep floating through your bloodstream, never entering the cells.

With diabetes, your body either can't make insulin, can't make enough insulin, or has developed a resistance to your insulin that prevents glucose from being moved into your cells. This can cause your cells to starve as the glucose levels in your blood rise and create a host of other problems.

What Does It Mean to Have High Blood Sugar?

Glucose levels in your bloodstream are normally regulated by your body and the insulin it makes. Insulin moves glucose into cells as they need it and stores the rest to use later.

When you have diabetes, either your body isn't making any or enough insulin to move sugar into your cells, or there is more sugar in your blood than your body can process. This leads to a state called hyperglycemia, or high blood sugar.

When glucose is trapped in your blood and can't enter your cells, several things can happen. If the problem is a lack of insulin or decreased sensitivity to insulin, the glucose stays in your blood and is unable to enter the cell and, therefore, starving your cells.

Symptoms of high blood sugar can include:

  • Excessive thirst or hunger
  • Blurry vision
  • Fatigue
  • Increased urination
  • Headache

If you address your blood sugar level right away, these symptoms should subside. But blood sugar levels that remain high for most of the time, or become excessively high sometimes, can cause more serious complications.

Why Is High Blood Sugar so Bad?

Think of the glucose in your body as sugar in a gas tank of a car. Over time, this glucose can clog and slow down other systems like the engine, making them work less efficiently.

One example is the kidneys. Your kidneys are made up of a web of delicate filters, and too much glucose can clog these filters, making them less effective. Over time, high blood sugar can lead to kidney disease or even kidney failure.

Other complications of long-term uncontrolled high blood sugar can include:

If your blood sugar becomes excessively high, you may also experience a problem called diabetic ketoacidosis. This happens when your body isn't making or responding to insulin. Unable to enter the cell, this glucose builds, and your cells start to starve.

To get the energy they need, cells start to consume fats stored in your body, releasing a chemical called ketones in the process. As ketones build in your body, they upset your chemical balance, resulting in the life-threatening condition ketoacidosis.

Symptoms of ketoacidosis include:

  • Fruity smelling breath
  • Shortness of breath
  • Very dry mouth
  • Nausea
  • Vomiting
  • Weakness
  • Fatigue

You must get medical attention right away if you blood glucose reaches excessive levels or you have any of the above symptoms.

What About Low Blood Sugar?

Low blood sugar, or hypoglycemia, happens when your body doesn't release sugars that your body stores. If you do not have diabetes, this can happen if you haven't eaten and there is a lack of glucose in your blood.

Symptoms of low blood sugar include:

  • Dizziness
  • Shakiness
  • Sweating
  • Nausea
  • Confusion

It's possible to lose consciousness or even become comatose if your blood glucose levels become dangerously low. For people with diabetes, finding the right balance between high and low blood sugar is crucial.

Blood Glucose Tests

Keeping your blood glucose levels in an acceptable range is the most important part of diabetes management regardless of what type of diabetes you have.

There are four types of blood glucose tests that might be used to check your blood sugar.

  • Fasting plasma glucose test: This test is done in a lab or medical facility with blood taken from a vein in your arm. This test is a very accurate measurement of your blood sugar without the influence of anything you have recently eaten or drunk. However, this test must be done first thing in the morning after an eight-hour fast—or eight hours of nothing to eat and only small sips of water.
  • HbA1C test: This is another test that is done in a lab or medical office with a sample of blood from your vein. You don't need to fast for this test. Instead of measuring your blood sugar level at a given time, this test analyzes different types of red blood cells called hemoglobin to create an average measurement of your blood glucose level over the past two or three months. This test is useful to see how you are managing your diabetes every day, and not just on the day of your test.
  • Oral glucose tolerance test: This test takes several hours to complete and is also done in a lab with a sample of blood from your vein. The test is done in several parts, with the first blood draw being done after an eight-hour fast. After the first test, you are given a sugary drink, and then your blood is rechecked several more times and different intervals. This test is useful in seeing how well your body is responding to the insulin it makes and is often used to diagnose type 2 diabetes, in particular.
  • Random or non-fasting glucose test: These tests can be done anywhere and at any time. Using a home blood glucose monitor and testing supplies, you use a small device—usually on your finger—to draw out a small drop of blood. The machine analyzes the glucose level in this sample and gives you an immediate result. This test is helpful for monitoring your blood sugar throughout the day, especially if you are taking medications like insulin to help control your diabetes.


Most of these glucose tests will happen in a lab or medical facility and you will be given specific instructions on when to arrive and how long to fast—if at all—before your test.

Home testing with the random plasma glucose test is where most people face problems. Getting in the habit of checking your blood sugar and the process of poking your finger can be intimidating. Your healthcare provider should offer you diabetes education if you are newly diagnosed.

Education is the first step in preparing for diabetes testing, and the next is to collect your supplies. Your healthcare provider or educator should walk you through the steps to get you the equipment you need when you are diagnosed with diabetes. Medicare, Medicaid, and most health insurance companies cover the bulk of the supplies you will need to test your blood sugar regularly.

If you have diabetes, how often you check your blood sugar can depend on the type of diabetes you have, and what medications you are using to manage your condition.

For most people with diabetes, blood glucose testing is recommended at these times of the day:

  • When you wake up
  • Before a meal
  • Two hours after a meal
  • At bedtime

Your doctor may also suggest additional testing times.

To do this testing, you will need the following supplies:

  • A blood glucose monitor
  • A lancet (small device that pokes through your skin to produce a drop of blood)
  • Alcohol pads for cleaning your finger before the test, and for cleaning your testing supplies
  • Testing strips on which you will place the drop of blood for testing in the machine


The process of testing your blood sugar may be different depending on what machine you have. Your healthcare provider should go over how to use your device with you, and may ask you to demonstrate how to use it. Always follow the specific manufacturer instructions for your device.

For most machines, the overall process is similar, including:

  1. With freshly washed hands, insert an unused testing strip into your blood glucose monitoring device.
  2. Wipe your finger with an alcohol pad and allow it to dry.
  3. Use the lancet, preferably on the side of a finger where the skin is thinner, to get a drop of blood.
  4. Touch the edge of the test strip to the drop of blood. The test strip will absorb the blood and begin testing.
  5. Once the machine is done analyzing, the machine will display a result. This number is your blood glucose measurement.

Side Effects

While some people are sensitive to having blood drawn in a lab, the drop used for home testing is so small that you should not experience any side effects. Over time, people who test their blood sugar regularly or frequently may have sore fingers, or marks on their fingers from testing.

Lancets are spring-loaded to reduce pain with testing, but you may also want to alternate sites to avoid having sore spots. You can use other fleshy areas besides the fingers for testing, like the forearm or thigh if you need to.

If you require frequent blood sugar checks, or you need a more constant watch over your blood glucose, you can also talk to you doctor about a continuous blood glucose monitoring device.


Your doctor may give you specific goals but the general range for a healthy blood glucose level is between 70 milligrams per deciliter (mg/dL) and 99 mg/dL on a plasma test or below 5.7% on an HbA1C test.

If you have lab testing done, your healthcare provider will talk to you about the results and what they mean for you. Examples of normal ranges can be found below.

Blood Glucose Readings

Fasting blood sugar test

  • Normal: 99 mg/dL and below
  • Prediabetes: 100–125 mg/dL
  • Diabetes: 126 mg/dL and above

HbA1C test

  • Normal: 5.7% and under
  • Prediabetes: 5.7%–6.4%
  • Diabetes: 6.5% and above

Oral glucose test

  • Normal: 140 mg/dL and below
  • Prediabetes: 140–199 mg/dL
  • Diabetes: 200 mg/dL and above

When you are testing at home, you are usually given target ranges you should try to maintain. Typical diabetes goal ranges for blood glucose levels are:

  • Between 80 and 130 mg/dL right before a meal
  • Below 180 mg/dL two hours after the start of a meal

If your blood sugar is too low—under 70 mg/dL, you need to do one of the following right away:

  • Chew four glucose tablets
  • Drink 4 ounces of fruit juice
  • Drink 4 ounces of regular soda
  • Chew four pieces of hard candy

Recheck your blood sugar 15 minutes after doing just one of these things, and repeat the process until your blood glucose level is over 70 mg/dL. If you are having problems increasing your blood glucose level, call a healthcare provider for help.

If your blood glucose level is too high—usually anything above 200 mg/dL for people with diabetes—you should follow the treatment plan prescribed by your healthcare provider. This may include drinking water, going for a walk, or taking insulin medication based on your individual blood glucose results.


Diabetes is a complex chronic disease. Strict control of your blood glucose levels through healthy diet and lifestyle choices, regular blood sugar monitoring, and medications are key to managing this condition and avoiding life-threatening complications. Work with a healthcare provider to create the best treatment plan for individual needs.

A Word From Verywell

Managing diabetes is not an easy task. It takes regular checks of your blood sugar and visits with your healthcare provider to find the regimen that works best for you. Making diet and lifestyle changes is important with managing diabetes, but it's not always enough.

If you have questions about your diabetes care, contact your healthcare provider or diabetes educator. They can also help you find programs to help cover the costs of your diabetes supplies and medications.

Frequently Asked Questions

  • How often should you take a blood sugar test?

    How often you should check your blood sugar can vary from one person to another. Most people living with diabetes check their blood sugar when they wake up, before eating, two hours after a meal, and before bedtime.

  • How can you lower your blood sugar naturally?

    A healthy diet and lifestyle can help you lower your blood sugar. Everything you eat and drink eventually breaks down to glucose, so cutting out sugar alone isn't enough. Talk to your healthcare provider about a diabetic diet if you have diabetes or are prediabetic. It's unlikely to reverse a diagnosis of diabetes using diet alone, but it can help you keep prediabetes from becoming diabetes.

  • Can you test blood sugar at home?

    If you have diabetes, you can—an absolutely should—check your blood sugar regularly at home. Your diet isn't the only thing that can affect your blood sugar—stress, medications, illness, and exercise can also make your blood glucose levels fluctuate. Regular monitoring can help you stay on top of these changes before they get out of hand.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. What is diabetes?

  2. Medline Plus. Blood sugar.

  3. Medline Plus. Hyperglycemia.

  4. Cleveland Clinic. Hyperglycemia.

  5. American Diabetes Association. Hyperglycemia.

  6. Medline Plus. Hypoglycemia.

  7. National Institutes of Health. Know your blood sugar numbers: Use them to manage your diabetes.

  8. American Diabetes Association. The big picture: Checking your blood sugar.

  9. Centers for Disease Control and Prevention. Diabetes tests.

By Rachael Zimlich, BSN, RN
Rachael is a freelance healthcare writer and critical care nurse based near Cleveland, Ohio.