A blood glucose test measures the sugar (glucose) circulating in your bloodstream.
Blood glucose tests are common and can be ordered or given by many healthcare providers. However, an endocrinologist (doctors who specialize in hormone-related conditions) may be a provider to help you manage your glucose levels based on your test results.
Your blood glucose level shows how well your body processes glucose from food into energy. Providers can order them as a screening tool during checkups or prenatal visits (around 24 and 28 weeks of pregnancy) or to diagnose and monitor people with prediabetes or diabetes.
With diabetes, your body doesn’t produce enough insulin or use it effectively, causing blood glucose to rise. Insulin is a hormone released by the pancreas to help glucose enter your cells. Monitoring your glucose when you have diabetes helps prevent complications such as eye problems, heart disease, kidney failure and nerve damage.
Risk factors for diabetes include a family history, being older than 45, and gestational diabetes (diabetes during pregnancy). Other potential risk factors include heart disease or stroke, high blood pressure, and obesity.
Your doctor may also order blood glucose tests if you have symptoms that suggest it hyperglycemia (high blood sugar). These include blurred vision, excessive thirst, fatigue, frequent urination, headaches and unexplained weight loss.
Blood glucose tests are also revealing hypoglycemia (low blood sugar). Symptoms include blurred vision, confusion, dizziness or fainting, irritability, fast heart rate, tremors, and sweating.
In addition to diabetes, health conditions that may require blood glucose testing include:
- Autoimmune disorders
- Critical illness
- Gestational diabetes
- Diseases of the heart, kidneys or liver
- Hormonal imbalance
- Insulin resistance
- Drug-induced hyperglycemia (from some antibiotics, steroids, or heart medications)
- Problems with the thyroid, pancreas, pituitary or adrenal glands (glands that secrete or regulate hormones)
There are several types of glucose tests. They serve special purposes in monitoring blood sugar levels. Here is an overview of the tests:
- capillary: Blood from finger stick (or earlobe, forearm, heel or palm)
- Continuously: A sensor under the skin continuously monitors glucose
- post: Testing after not eating for eight hours
- Glucose tolerance: Testing before and after consumption of glucose solution
- Hemoglobin A1c (HbA1c): Long-term (three-month) average
- Random (random): Testing anytime, regardless of food intake
- Point of concern: Get results quickly from handheld devices
- Postprandial: One to two hours after eating
- venous: A healthcare worker draws blood from a vein
For the fasting test, do not eat or drink anything except water for eight hours before the test. A non-fasting random blood glucose test does not require fasting.
If you are having a blood draw, wear loose clothing with easy access to the upper arm. Having blood drawn is generally safe, but it can be stressful. Consider bringing someone for support. Afterwards, you may feel dizzy if you have also done an oral glucose tolerance test. Consider having someone drive you.
You may need to fill out your medical history or insurance information before the test. Bring your identification form and insurance card (if you have one). Most insurance plans cover the blood glucose test. If you need financial help, ask your healthcare team about assistance programs.
Capillary blood glucose (CBG) takes a minute or two and can occur in any setting. Venous blood glucose tests take a few minutes and are done in a clinical setting.
During the test
CBG includes a lancet (a small, sharp needle), a test strip, and a glucose meter. Your healthcare team can do this, but they can also teach you how to do a finger stick at home.
Wash your hands, collect your supplies, and insert the test strip into your glucose meter. Use the lancet to prick the side of the third or fourth finger or another location such as the forearm or earlobe. Place a drop of blood on the test strip and clean the puncture site. The meter will display your blood glucose level within seconds.
During a lab blood glucose test, you’ll sit in a chair while a healthcare professional uses a tiny, sterile needle to draw blood from your arm. You may feel a slight sting when the needle goes in or out. The person drawing your blood will:
- Place a wide rubber band on your upper arm
- Clean the skin with an antiseptic such as alcohol
- Insert the needle into your vein
- Draw the blood into a test tube
- Remove the needle
- Apply pressure and bandage
- Send the blood sample to the laboratory
After the test/post-test
After the CBG, you or your doctor should record the glucose reading and dispose of the lancet and test strip in a sharps container. After the venous blood glucose test, you can usually leave immediately.
If needles make you nauseous, take a moment to rest before riding. Depending on the results, your doctor may suggest further testing, changes in medication, or referral to a specialist.
It is essential to clean the area before using the lancet or needle to avoid infection. Otherwise, both tests are generally safe.
With a finger stick, the lancet can cause the tip of the finger to sting, and it may be slightly tender or bruised afterward. Avoiding the first finger and thumb reduces the risk of pain. During the blood draw, you may feel a slight pinch or notice a bruise where the needle was, but it usually goes away quickly.
CBG with a glucometer gives results in a few seconds. Laboratory vein extraction results may take a day or two. Your healthcare team will share the results via the patient portal, phone call, text, letter or follow-up.
Depending on your results, your doctor may recommend further testing, lifestyle changes, medication, monitoring, or a referral to a specialist. Below are typical ranges of blood glucose levels.
| Blood glucose level | |
|---|---|
| Fasting Ranges | Ranges without fasting |
| low: Below 70 mg/dL | N/A |
| normally: 70-99 mg/dL | normally: Less than 140 mg/dL |
| limit: 100-125 mg/dL | limit: 140-199 mg/dL |
| high: 126 mg/dL or more | high: 200 mg/dL or more |
Your doctor may aim for different blood sugar levels based on your age or medical history. A pre-meal blood sugar target for those who already have diabetes is likely to be:
- 90-180 mg/dL for ages 6-12
- 90-130 mg/dL for those 13 and older
A normal range indicates that there are no problems with blood sugar at the time of the test. A low level indicates hypoglycemia (low blood sugar). For those with diabetes, check with your doctor; your target goal may be closer to 7 or lower.
Inconclusive results may occur due to temporary fluctuations in blood sugar or test error. Borderline high levels can mean prediabetes. A high level may mean you have diabetes, but one high level does not always mean this. If you have inconclusive, borderline, or high results, your doctor will likely suggest another glucose or hemoglobin A1C test.
| A1C and glucose tolerance range | |
|---|---|
| Hemoglobin A1C | Glucose tolerance |
| normally: Below 5.7% | normally: Less than 140 mg/dL 2 hours after the test |
| limit: 5.7-6.4% | limit: 140-199 mg/dL |
| high: 6.5% or more | high: 200 mg/dL or more |
Many people only experience symptoms of high blood sugar when their levels are 250 mg/dL or higher. Some are more sensitive and may have symptoms before their levels reach 250 mg/dL. High levels require immediate medical attention. If you have diabetes and take insulin, follow your doctor’s instructions.
A blood glucose test measures the amount of sugar circulating in your bloodstream. It’s safe and only takes a few minutes. The test may involve a rapid capillary blood glucose and glucometer or a provider drawing blood from a vein in your arm.
Blood sugar levels help your doctors monitor and treat hypoglycemia (low blood sugar) and hyperglycemia (high blood sugar, usually due to diabetes).
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