Fasting Blood Glucose Test

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KEY POINTS

• The fasting blood glucose test (FBS) measures the amount of glucose (sugar) in your child’s blood when your child has not had anything to eat or drink for at least 8 hours. The most common use of this test is to check for diabetes.
• Your healthcare provider may poke your child’s finger with a small needle (lancet) or take a small amount of blood from your child’s arm with a needle. The blood is sent to a lab.
• Talk to your child’s healthcare provider about what the test results mean and ask any questions you have.

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What is the fasting blood glucose test?

The fasting blood glucose test (FBS) measures the amount of glucose (sugar) in your child’s blood when your child has not had anything to eat or drink for at least 8 hours. It is also called a fasting plasma glucose test.

Why is this test done?

The most common use of this test is to check for diabetes. The body breaks down some of the foods your child eats into glucose. The blood carries the glucose to the cells of your child’s body. Your child needs some glucose in the cells for energy, but too much glucose in the blood is not good for your child’s health. Blood glucose that stays high is the main problem of diabetes.

How do I prepare my child for this test?

Your healthcare provider will tell you when your child should stop eating and drinking before the test. In most cases your child should eat nothing and drink nothing but water for at least 8 hours before the test. Make sure your child drinks plenty of water before the test.

Your child may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that your child is taking. Ask your provider before stopping any of your child’s regular medicines.

Talk to your child's healthcare provider if you have any questions about the test.

How is the test done?

Your healthcare provider may poke your child’s finger with a small needle (lancet) and fill a small tube with the blood, or take a small amount of blood from the arm with a needle. The blood is sent to a lab.

Having this test will take just a few minutes.

Ask your healthcare provider when and how you will get the result of the test.

What does the test result mean?

Blood glucose level may be higher than normal (hyperglycemia) if:

• Your child has prediabetes (the blood glucose level is higher than normal, but not quite high enough to be called diabetes).
• Your child has diabetes.
• If your child already has diabetes
  • Your child has not been taking prescribed medicine correctly.
  • Your child is not controlling the diabetes.
  • Your child has not been following a food or activity plan.
• Your child has kidney or liver disease.
• Your child's pancreas is inflamed. The pancreas is an organ in your upper belly that makes insulin.
• Your child's body is severely stressed from a bad infection, surgery, or injury.
• Your child is taking certain medicine, such as antibiotics, steroids, or asthma medicine that can raise blood glucose.
• Your child's blood glucose level may be lower than normal (hypoglycemia) if:
• Your child has diabetes and:
  • The dose of insulin or other medicine used to control the diabetes is too high.
  • Your child took medicine for diabetes and then exercised too much.
• Your child's thyroid, pituitary, or adrenal glands are not working normally. These glands make hormones, which are chemicals that help with things such as growth, development, and control of blood pressure and blood glucose.
• Your child has liver disease.
• Your child has problems absorbing food.
• Your child is not getting the nutrients needed from food.

What if my child's test result is not normal?

Test results are only one part of a larger picture that takes into account your child's medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about the result and ask questions, such as:

• If your child needs more tests
• What kind of treatment your child might need
• What lifestyle, diet, or other changes your child might need to make