A blood sugar test can be used to determine the amount of glucose in the blood. It may be used to diagnose diabetes or to help those with diabetes check their blood sugar and insulin levels.

A blood sugar test is a procedure that measures the amount of sugar, or glucose, in your blood. A doctor may order this test to help diagnose diabetes. People with type 1 and type 2 diabetes also use this test to manage their condition.

Type 1 diabetes occurs when the cells in the body responsible for producing insulin are destroyed. Type 2 diabetes occurs when your body becomes resistant to insulin and no longer uses it effectively. Both types can result in high blood sugar if they’re not managed well.

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

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

If you have not been diagnosed with diabetes, a doctor may also order a blood sugar test as part of a routine checkup. They may also be looking to see if you have diabetes or prediabetes, a condition where your blood sugar levels are higher than typical.

People may need to be tested if they have symptoms of diabetes or if they have certain risk factors.

Risk factors for diabetes

You may have more likely to get type 1 diabetes if you:

  • are a teenager or younger
  • have a family member with the condition
  • have certain genes that give you a genetic predisposition

Your risk for type 2 diabetes may increase if you:

  • are age 35 years or older
  • are overweight
  • are not physically active
  • have a family history of diabetes
  • have a history of insulin resistance or have prediabetes
  • have a history of gestational diabetes or gave birth to a baby who weighed over 9 pounds
  • have high blood pressure, high triglycerides, or high cholesterol
  • have a history of stroke or hypertension

Research has shown that type 2 diabetes occurs more often in adults with Native American, African American, Hispanic or Latino American, Asian American, or Alaskan or Pacific Islander ancestry than non-Hispanic white adults.

They may also be more likely to experience decreased quality of care and increased barriers to prevention and self-management support due to healthcare disparities.

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

A 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 diabetic ketoacidosis, a life threatening condition that’s often a concern for those with type 1 diabetes. Hyperglycemia over a long period can increase your risk of neuropathy (nerve damage), along with heart, kidney, and eye diseases.

Diabetic ketoacidosis vs. ketosis

Diabetic ketoacidosis happens when your blood sugar is very high and ketones reach dangerous levels in your body.

Ketosis occurs when the body uses fat for energy. This can happen as a result of an extremely low carbohydrate diet or from fasting.

Was this helpful?

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.

You can take a blood sugar test two ways.

People who are monitoring or managing their diabetes may use a glucometer for daily testing. This method involves pricking the skin (usually a finger) with a lancet to draw a blood sample, applying the blood on a test strip, and inserting it into the monitor.

The second method involves a healthcare professional drawing a blood sample and sending it to a lab to be evaluated.

Blood samples are generally used to screen for diabetes. A doctor will typically order a fasting blood sugar (FBS) test, which measures your blood sugar levels.

They may also order a glycosylated hemoglobin test called a hemoglobin A1C test. The test results reflect your blood sugar levels over the previous 90 days. The results will show if you have prediabetes or diabetes. In people already diagnosed with diabetes, this test can monitor how well their diabetes is managed.

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

Type 1 diabetes

According to research, 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
  • 2–3 hours after eating
  • before sleeping
  • if you feel any symptoms of low or high blood sugar

High blood sugar

According to the American Diabetes Association (ADA), you should 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. This may be a sign that you may need to modify your treatment plan.

If your diabetes is managed well but you still have 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 a doctor to decide how to get your blood sugar levels back into target range.

Low blood sugar

According to the ADA, you should 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

Severe symptoms like delirium, seizures, or unconsciousness can be symptoms of low blood sugar or insulin shock. If you’re on daily insulin injections, ask your doctor about glucagon, a prescription medication 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.


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

A doctor may recommend testing your blood sugar regularly if you have gestational diabetes. Testing helps with keeping you aware of your blood sugar levels so you can take necessary steps 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. You may also not need home testing if you’re taking medications that are not associated with low blood sugar.

A healthcare professional will insert a needle into your vein and draw blood to get a sample. You may need to fast for 8 hours before the FBS test. Your healthcare professional will let know if you need to fast.

You do not need to fast before the A1C test.

Home tests

You can take blood sugar tests at home with a glucometer or with a blood test. The exact steps for finger sticks or glucose meter tests vary depending on the type and brand of test. Your home kit will provide instructions on use.

Typically, the procedure involves pricking your finger with a lancet and putting the blood on a testing strip. The strip is then inserted into a glucometer. Your results usually show on the screen in 10 to 20 seconds.

Continuous glucose monitoring (CGM)

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

The sensor can last several days to a week before you need to replace it. You’ll still have to check your blood sugar with a meter to calibrate your CGM every several days to 2 weeks.

CGM devices are not as reliable for acute problems like identifying low blood sugar levels. For the most accurate results, you should use a glucometer or a blood test.

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

A doctor may 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 better manage 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 working with your healthcare professional to adjust your treatment for better results.

Diagnostic results

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

Without diabetesPrediabetesDiabetes
Fasting Plasma Glucoseless than or equal to 99 mg/dLbetween 100–125 mg/dLgreater than or equal to 126 mg/dL
A1Cunder 5.7%5.7–6.4%greater than or equal to 6.5%

A doctor can help create a treatment plan if your results suggest prediabetes or diabetes.

Read this article in Spanish.