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Blood Sugar Test

What is a blood sugar test?

A blood sugar test is a procedure that measures the amount of sugar, or glucose, in your blood. Your doctor may order this test to help diagnose diabetes. And people with diabetes can use this test to manage their condition.

Blood sugar tests provide instant results and let you know the following:

  • your diet or exercise routine needs to change
  • your diabetes medications or treatment is working
  • your blood sugar levels are high or low
  • your overall treatment goals for diabetes are manageable

Your doctor may also order a blood sugar test as part of a routine checkup. Or to see if you have diabetes or prediabetes, a condition where your blood sugar levels are higher than normal.

Your risk for diabetes increases if any of the following factors are true:

  • you are 45 years old or older
  • you are overweight
  • you don’t exercise much
  • you have high blood pressure, high triglycerides, or low good cholesterol levels (HDL)
  • you have a history of gestational diabetes or giving birth to a baby who weighed over 9 pounds
  • you have a history if insulin resistance
  • you are Asian, African, Hispanic, Pacific Islander, or Native American
  • you have a family history of diabetes

Checking your blood sugar levels can be done at home or at a doctor’s office. Read on to learn more about blood sugar tests, who they are for, and what the results mean.

What does a blood sugar test do?

Your doctor may order a blood sugar test to see if you have diabetes or prediabetes. The test will measure the amount of glucose in your blood.

Your body takes carbohydrates found in foods like grains and fruits and converts them into glucose. Glucose, a sugar, is one of the body’s main sources of energy.

For people with diabetes, a home test helps monitor blood sugar levels. Taking a blood sugar test can help determine your blood sugar level to see if you need to adjust your diet, exercise, or diabetes medications.

Low blood sugar (hypoglycemia) can lead to seizures or a coma if left untreated. High blood sugar (hyperglycemia) can lead to ketoacidosis, a life-threatening condition that’s often a concern for those with type 1 diabetes. Ketoacidosis occurs when your body starts using only fat for fuel.

What are the risks and side effects of a blood sugar test?

A blood sugar test has low to no risks or side effects.

You may feel soreness, swelling, and bruising at the puncture site, especially if you’re drawing blood from a vein. This should go away within a day.  

Types of blood sugar tests

You can take a blood sugar test two ways. People who are monitoring or managing their diabetes use a glucometer, which pricks your finger, for daily testing. The other method is drawing blood.

Blood samples are generally used to screen for diabetes. Your doctor will order a fasting blood sugar (FBS) test, which measures your blood sugar levels, or a glycosylated hemoglobin. Or your doctor will order a hemoglobin A1C test, which reflects your blood sugar levels over the last 90 days. The results will show if you have prediabetes or diabetes.

When to test blood sugar

When and how often you should test your blood sugar depends on the type of diabetes you have and your treatment.

For type 1 diabetes

According to the American Diabetes Association (ADA), if you’re managing type 1 diabetes with multiple dose insulin or an insulin pump, you’ll want to monitor your blood sugar before:

  • eating a meal or snack
  • exercising
  • sleeping
  • critical tasks like driving or babysitting

High blood sugar

You’ll want to check your blood sugar levels if you have diabetes and feel increasing thirst and the urge to urinate. These could be symptoms of high blood sugar and you may need to modify your treatment plan. 

If your diabetes is well-controlled but you still have these symptoms, it may mean you’re getting sick or that you’re under stress.

Exercising and managing your carbohydrate intake may help with lowering your blood sugar levels. If these changes don’t work, you may need to meet with your doctor to decide how get your blood sugar levels back into target range.

Low blood sugar

Check your blood sugar levels if you feel any of the following symptoms:

  • shaky
  • sweaty or chilly
  • irritated or impatient
  • confused
  • lightheaded or dizzy
  • hungry and nauseous
  • sleepy
  • tingly or numb in the lips or tongue
  • weak
  • angry, stubborn, or sad

Some symptoms like delirium, seizures, or unconsciousness can be symptoms of low blood sugar or insulin shock. Those on daily insulin injections should ask their doctor about glucagon, a prescription medicine that can help if you’re having a severe low blood sugar reaction.

You can also have low blood sugar and show no symptoms. This is called hypoglycemia unawareness. If you have a history of hypoglycemia unawareness, you may need to test your blood sugar more often.

Pregnant women

Some women develop gestational diabetes during pregnancy. This is when hormones interfere with the way your body uses insulin. It causes sugar to accumulate in the blood.

Your doctor will recommend testing your blood sugar regularly if you have gestational diabetes. This is to make sure that your blood glucose level is within a healthy range. Gestational diabetes usually goes away after childbirth.

No scheduled testing

Home testing may be unnecessary if you have type 2 diabetes and have a diet- and exercise-based treatment plan. Or if you are taking medications that aren’t associated with low blood sugar.

How is a blood sugar test administered?

To get a sample, your doctor will insert a needle into your vein and draw blood. Your doctor will ask you to fast for 12 hours before the FBS test. You don’t need to fast before the A1C test.

Home tests

You can take blood sugar tests at home with a glucometer. The exact steps of finger stick glucose meter tests vary depending on the type of glucose meter. Your home kit will have instructions.

The procedure involves pricking your finger and putting the blood on a glucose meter strip. The strip is usually already inserted into the machine. Your results will show on the screen in 10 to 20 seconds.

Continuous glucose monitoring (CGM)

You can also wear a device for continuous glucose monitoring (CGM). The glucose sensor is inserted under the skin and reads the sugar in your body tissue continuously. It alerts you whenever your blood sugar is too low or too high.

The sensor can last several days to a week before it needs to be replaced. You’ll still have to check your blood sugar with a meter twice a day to calibrate your CGM.

CGM devices aren’t as reliable for acute problems like identifying low blood sugar levels. For the most accurate results you should use your glucometer.

What do the results of the blood sugar test mean?

Depending on your condition and the timing of your test, your blood sugar levels should be in the target ranges listed below.

TimePeople without diabetesPeople with diabetes
Before breakfastunder 70-99 mg/dL80-130 mg/dL
Before lunch, dinner, and snacksunder 70-99 mg/dL80-130 mg/dL
Two hours after eatingunder 140 mg/dLunder 180 mg/dL
Before sleepingunder 120 mg/dL90-150 mg/dL

Your doctor will provide a more specific target range for your blood sugar levels, depending on the following factors:

  • personal history
  • how long you’ve had diabetes
  • presence of diabetes complications
  • age
  • pregnancy
  • overall health

Tracking your blood sugar levels is one way to take control of your diabetes. You may find it helpful to log your results in a journal or app. Trends like continuously having levels that are too high or too low may mean adjusting your treatment for better results.

Diagnostic results

The table below shows what your blood sugar test results mean:

FBS testunder 100 mg/dLbetween 110–125 mg/dLgreater than or equal to 126 mg/dL
A1C testunder 5.7 percent5.7-6.4 percentgreater than or equal to 6.5 percent

Your doctor will be able to help create a treatment plan if your results suggest prediabetes or diabetes.

Content licensed from:

Written by: MaryAnn DePietro and Valencia Higuera
Medically reviewed on: Aug 02, 2016: Peggy Pletcher, MS, RD, LD, CDE

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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