If you have symptoms such as severe increased thirstfrequent urinationunexplained weight lossincreased hungerand tingling in your hands or feetyour doctor may run a test for diabetes.
According to the CDCsome 38 million children and adults in the U.S.or over 11% of the populationhave diabetes today. Yetmillions of Americans are unaware that they have diabetes because they may not have symptoms.
To confirm the diagnosis of type 2 diabetesyour doctor will order a fasting plasma glucose test or a casual plasma glucose.
Both of these tests measure the amount of glucose (or sugar) in your blood. Measuring your blood glucose levels (also called blood sugar levels) helps your doctor diagnose diabetes. The tests are performed at your doctor’s officelabor hospital and involve either a simple blood draw or a finger prick.
Blood Sugar Levels
Blood glucoseor blood sugaris your body’s main source of energy. Your body changes the carbohydrates you eat or drink into glucoseor sugarwhich provides energy to all of the cells in your body. Your liver also makes and stores glucose. To keep your blood sugar levels in a normal rangeyour body uses the glucose stored in your liver if you haven’t eaten for some time.
Your diet influences the level of glucose in your blood. If you eat carbohydrate-heavy or sugary foods and drinksyour blood glucose levels will be high. Eating too few carbohydrates will cause low blood glucose levels. A healthybalanced diet helps maintain normal blood glucose values.
Insulin is an important hormoneor chemical messengerthat helps keep blood sugar levels in a healthy range. Problems with how your body produces or uses insulin cause poor blood glucose control and diabetes.
Normal blood sugar levels
A normal fasting blood sugar level is 99 milligrams per deciliter (mg/dL) or below. Fasting means that you haven’t eaten for 8-10 hours before the test. Your blood sugar level will rise after you eat and then fall after about an hour.
If you have managed diabetesa normal fasting blood glucose level is 80-130 mg/dL. A normal level 1-2 hours after the start of a meal is less than 180 mg/dL.
High blood sugar levels
High blood sugar levels mean there is too much glucose in your blood. This happens when your body doesn’t make enough insulin or can’t use it properlywhich leads to hyperglycemiaalso called high blood sugar.
Untreated hyperglycemia for a long period can damage your nervesblood vesselstissuesand organs. That’s why it's important to have a blood glucose test done if you have any early symptoms of diabetes such as severe increased thirstfrequent urinationand unexplained weight loss.
A fasting blood glucose level of 100-125 mg/dL is high and usually indicates prediabetes. If you have a fasting blood glucose level greater than 125 mg/dL on two separate testsyou’ll likely be diagnosed with diabetes.
Testing Blood Sugar Levels
There are a few different tests doctors use to check your blood glucose levels and diagnose diabetes. Some tests are done on an empty stomach; for othersthe last time you ate is not important. Your doctor will recommend the most suitable test based on your symptoms and circumstances. Here are the different types of blood glucose tests.
Fasting plasma glucose test
The fasting plasma glucose test (FPG) is one way your doctor may check for diabetes.
You will not be allowed to eat anything for at least 8 hours before taking the fasting blood glucose test. Because of thisyour doctor might recommend you have the test performed first thing in the morning before breakfast.
During a fasting blood glucose testa health care provider such as a phlebotomist or medical assistantwill use a small needle to draw blood from a vein in your arm. Your blood sample will be measured in a lab and you’ll usually receive results after a few days.
Blood glucose test results
Normal fasting blood glucose is less than 100 mg/dL for people who do not have diabetes. Howeverif you have normal fasting blood sugarbut you have risk factors for diabetes or symptoms of diabetesyour doctor may decide to do a glucose tolerance test (see below) to be sure that you do not have diabetes.
Some people have a normal fasting blood sugar readingbut their blood sugar rapidly rises as they eat. These people may have prediabetesalso called impaired glucose tolerance. If you have prediabetes you are at higher risk of developing Type 2 diabetes.
Casual plasma glucose test
The casual (or random) plasma glucose test is another method of diagnosing diabetes. Your blood sugar is tested regardless of when you last ate. You are not required to avoid eating before the test.
A glucose level greater than 200 mg/dL may indicate diabetesespecially if the test is repeated at a later time and shows similar results. Your doctor may recommend this test if you have severe diabetes symptoms.
Glucose tolerance test
The oral glucose tolerance test (OGTT) is yet another method used to detect diabetes. Your doctor will perform this test to diagnose type 2 diabetesprediabetesand gestational diabetes (diabetes that develops during pregnancy).
This is a longer test with a few separate blood draws. Firsta health care provider will collect a fasting blood sample. Nextyou’ll drink a sugary liquid. You’ll provide another blood sample 1 and 2 hours later. This test tells your doctor how your body breaks down sugar. If your blood glucose level is 200 mg/dL or higher at the 2-hour markyour body is not processing sugar properly and you likely have diabetes.
If you are pregnantyou’ll be screened for gestational diabetes with a glucose challenge test. Similar to the OGTTyou’ll provide a baseline blood samplethen drink a sugary liquid and provide another sample 1 hour later. You don’t need to fast for this test. If your blood glucose level is high (135-140 mg/dL) at the 1-hour markyour doctor will perform the OGTTtaking blood samples every hour for 3 hours to check whether or not you have gestational diabetes.
Hemoglobin A1c test
The hemoglobin A1c test (also called the glycated hemoglobin testHbA1cor A1c) measures your average blood sugar level over the past 2-3 months. It’s an important blood glucose test used to diagnose type 1 and type 2 diabetesas well as determine how well your blood sugar is being controlled if you have diabetes.
You don’t need to fast for the A1c test. A health care provider will collect your blood from a vein or by pricking your finger.
A high A1c shows a poor level of blood sugar control. A normal value is less than 5.7%. Prediabetes is diagnosed at 5.7%-6.4%. If your A1c level is 6.5% or higher on two separate testsyou will likely be diagnosed with diabetes.
Along with the hemoglobin A1c testpeople with diabetes should have a dilated eye exam at least once a year as part of a complete eye exam. This important test can detect early signs of retinopathy (damage to blood vessels at the back of your eyes)which may have no symptoms at first. A foot exam once or twice a year — or at every doctor's visit — is also important to detect poor blood flow and sores that may not be healing. Early detection of eye and foot problems in diabetes allows your doctor to prescribe proper treatment when it is most effective.
Diabetes Testing in Children
Many children have no symptoms before they are diagnosed with type 2 diabetes. Most of the timediabetes is discovered when a blood or urine test taken for other health problems shows diabetes.
Talk to your doctor about your child's risk for diabetes. If your child's blood sugar tests are higher than normalbut not yet at the level of diabetes (called prediabetes)your doctor may instruct you to make specific diet and exercise changes to help your child avoid getting diabetes altogether. Children with type 2 diabetes or prediabetes are almost always overweight or obese.
Type 1 diabetes is often diagnosed in children and adolescents but can occur at any age. People with type 1 diabetes don’t produce any insulin and need injections of insulin to survive. This condition used to be called juvenile diabetes or insulin-dependent diabetes.
The risk factors for developing type 1 diabetes are:
- A parent or sibling with type 1 diabetes
- Certain genes that increase the risk
- Being of white non-Hispanic descent
- Exposure to certain viruses that trigger an autoimmune response
Symptoms of type 1 diabetes are unexpected and come on quickly. They include:
- Severe thirstalso called polydipsia
- Severe hungeralso called polyphagia
- Frequent urinationalso called polyuria
- Unexplained weight loss
- Fatigue or excessive sleepiness
- Irritability
- Fruity-smelling breath
Your doctor will perform the same blood glucose tests to check for type 1 and type 2 diabetes. If your symptoms suggest type 1 diabetesyour doctor will check your urine for ketones — an acid that shows your body is burning fat instead of glucose for energy. Ketones in your urine are a sign of type 1 diabetes. You’ll have another blood test to check for autoantibodies common in people with type 1 diabetes.
Understanding Your Diabetes Diagnosis
If you’re diagnosed with diabetesit’s possible to feel good and stay healthy despite your diagnosis. You can avoid major health problems by keeping your blood sugar levels in check. Keep your blood sugar levels in a healthy range by making good choices in the following areas:
Food. Eat a balanced diet and avoid sugary drinks (unless you have a low blood sugar level). Learn to count carbohydrates and be mindful of portion sizes to make sure you are eating the right amount and right types of food.
Exercise. Movement through regular exercise improves the way your body uses insulin. Talk with your doctor to come up with an exercise plan that includes safe blood glucose levels and a schedule that lines up with your meals and medicine.
Medicine. Take your medication as prescribed by your doctor. Tell your doctor about any problems or concerns you have about how your medicine is working.
Illness. Your blood sugar may be more difficult to control when you're sick. Have a plan for managing illnessesincluding what cold medicines you can take and how often you should check your blood sugar.
Stress. It's important to manage stress because stress hormones may cause blood sugar levels to rise. Have a plan to manage your stress with relaxing activities that you enjoy.
Blood sugar level monitoring
Regularly monitoring your blood sugar levels is an important part of diabetes managementespecially if you take insulin to control your diabetes. Your doctor will teach you how to monitor your blood glucose at home using a glucose meter or continuous glucose monitor (CGM).
To use a glucose meteryou’ll prick your finger to produce a small drop of blood that is placed on a test strip in the meter. The meter will show your blood sugar level in seconds.
A CGM is a wearable medical device that measures your blood glucose levels 24 hours a day. This device includes a small sensor that’s inserted under your skin to measure blood sugar levels in your body.
Both options help monitor blood sugar levels for hyperglycemia (high blood sugar) or hypoglycemia (low blood sugar). It's important to check your blood sugar level to know how much insulin you need for hyperglycemia or how many carbohydrates to eat for hypoglycemia.
Takeaways
Doctors use many different blood glucose tests to diagnose diabetes including fasting plasma glucosecasual plasma glucoseglucose toleranceand hemoglobin A1c. A fasting plasma glucose test result of 125 mg/dL or higher or a glucose tolerance test of 200 mg/dL or higher usually means you have diabetes. You can be healthy and manage your diabetes by monitoring your blood glucose levels at hometaking your medicineand making other modest life changes.
Blood Glucose Test FAQs
How do you test for diabetes?
There are several blood glucose tests your doctor might use to test for diabetes. These include fasting plasma glucosecasual (random) plasma glucoseoral glucose toleranceand hemoglobin A1c. Some of the tests are done on an empty stomach. Your blood will be collected from a vein or finger prick.
What is normal HbA1c by age?
A normal hemoglobin A1c is less than 5.7% regardless of age.
Is 200 blood sugar normal after eating?
A blood sugar level of 200 mg/dL after eating may mean you have diabetes and should follow up with your doctor for further testing.
What is a normal glucose level?
A normal glucose levelno matter when you last ateis less than 200 mg/dL.
