For people at risk for or who’ve been diagnosed with diabetes, blood tests provide invaluable information about how your body is using glucose (blood sugar). This helps physicians assess and treat the condition. Some blood tests will be performed infrequently, while some have to be performed every day or even several times a day. 

Diagnosing Diabetes

Your physician will administer one or more blood tests to determine if you have diabetes:

  • Fasting Plasma Glucose Test (FPGT). The FPGT is the most common diabetes testing tool. Your physician will administer this test after you fast for eight hours. If your fasting plasma glucose (sugar) level is 126 mg/dl (milligrams per deciliter) or higher, you have diabetes. Your physician will likely confirm the diagnosis by repeating the test on another day.
  • Oral Glucose Tolerance Test (OGTT). After at least an eight hour fast, your physician or laboratory will draw your blood. Then they will give you a high-glucose drink and redraw your blood two hours later (the OGTT). If your glucose levels are between 140 and 199 mg/dl, you have impaired glucose tolerance. The OGTT is also the most common test used in pregnancy to diagnose gestational diabetes.
  • A1c test. The A1c test, also called hemoglobin A1c, HbA1c, or glycohemoglobin test, helps diagnose prediabetes and types 1 and 2. A1c shows your blood sugar average over the preceding two to three months. A result of 6.5 percent or higher indicates diabetes. If you score between 5.7 and 6.4 percent, you’re at risk for developing diabetes, and will likely be asked to repeat the test in a year.

Monitoring Diabetes

People with diabetes are generally required to monitor their blood sugar daily with an at-home blood glucose meter. These daily readings give you a snapshot of your blood sugar levels at any given moment. Once you are diagnosed, your physician will set target ranges for your daily blood sugar levels.

Keep a daily log of your results (date, time, results, medications, and dosages) and bring it when you see your physician. This information shows how your treatment plan is working and helps you identify factors (for example, food or stress) that affect your blood glucose levels.

How often you need to check your blood glucose levels depends on the type and severity of your diabetes. Patients with type 1 may need to test their blood glucose three or more times daily, often before or after meals and exercise and at bedtime. If you have type 2 diabetes, the frequency will depend on whether you take insulin.

Your physician will also continue to use the A1c test to monitor your blood glucose levels over time.

Other Tests

Checking your blood pressure and cholesterol levels regularly is also important. Elevated blood pressure or cholesterol can lead to serious complications, such as heart disease, stroke, or damage to your kidneys or eyes.

Amber Taylor, MD, director of the Diabetess Center at Mercy Medical Center, Baltimore, reviewed this article.


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"Diagnosing Diabetes and Learning About Prediabetes." American Diabetes Association. Last edited March 27, 2014. 

"Type 1 Diabetes." Mayo Clinic. August 02, 2014.