Type 1 Diabetes
There are three tests that can diagnose diabetes:
- Fasting plasma glucose (FPG)
- Oral glucose tolerance test (OGTT)
- Hemglobin A1C (A1C)
Fasting Plasma Glucose Test
The fasting plasma glucose (FPG) test has been the standard test for diagnosing diabetes. It is a simple blood test taken after 8 hours of fasting.
FPG levels indicate:
- Normal. 100 mg/dL (or 5.5 mmol/L) or below.
- Pre-Diabetes. (A risk factor for type 2 diabetes): Between 100 - 125 mg/dL (5.5 - 7.0 mmol/L).
- Diabetes.126 mg/dL (7.0 mmol/L) or higher
The FPG test is not always reliable, so a repeat test is recommended if the initial test suggests the presence of diabetes, or if the tests are normal in people who have symptoms or risk factors for diabetes. Widespread screening of patients to identify those at higher risk for diabetes type 1 is not recommended.
Oral Glucose Tolerance Test
The oral glucose tolerance test (OGTT) is more complex than the FPG and may overdiagnose diabetes in people who do not have it. Some doctors recommend it as a follow-up after FPG, if the latter test results are normal but the patient has symptoms or risk factors of diabetes. The test uses the following procedures:
- It first uses an FPG test.
- A blood test is then taken 2 hours later after drinking a special glucose solution.
OGTT levels indicate:
- Normal. 140 mg/dL or below.
- Pre-Diabetes. Between 140 - 199 mg/dL.
- Diabetes. 200 mg/dL or higher.
Patients who have the FPG and OGTT tests must not eat for at least 8 hours prior to the test.The oral glucose tolerance test is used to diagnose diabetes. The first portion of the test involves drinking a special glucose solution. Blood is then taken several hours later to test for the level of glucose in the blood. Patients with diabetes will have higher than normal levels of glucose in their blood.
Hemoglobin A1C Test
This test examines blood levels of glycosylated hemoglobin, also known as hemoglobin A1C (HbA1c). The results are given in percentages and indicate a person’s average blood glucose levels over the past 2 - 3 months. (The FPG and OGTT show a person’s glucose level for only the time of the test.) The A1C test is not affected by recent food intake so patients do not need to fast to prepare for it.
In 2010, the American Diabetes Association advised that the A1C test can be used as another option for diagnosing diabetes.
A1C levels indicate:
- Normal. Less than 5.7 percent.
- Pre-Diabetes. Between 5.7 - 6.4 percent.
- Diabetes. 6.5 percent or higher.
A1C tests are also used to help patients with diabetes monitor how well they are keeping their blood glucose levels under control. For patients with diabetes, A1C is measured periodically every 2 - 3 months, or at least twice a year. While finger prick self-testing provides information on blood glucose for that day, the A1C test shows how well blood sugar has been controlled over the past several months.
In general, most adult patients with diabetes should aim for A1C levels below or around 7%. Your doctor may adjust this goal depending on your individual health profile.
Goal A1C levels for children are:
- Between 7.5 - 8.5% for children under age 6 years
- Less than 8% for children age 6 - 12 years
- Less than 7.5% for children age 13 - 19 years
Schedule for A1C Monitoring:
- Every 6 months if diabetes is well controlled
- Every 3 months if not well controlled
The American Diabetes Association recommends that results from the A1C test be used as to calculate estimated Average Glucose (eAG). EAG is a relatively new term that patients may see on lab results from their A1C tests. It converts the A1C percentages into the same mg/dL units that patients are familiar with from their daily home blood glucose tests. For example, an A1C of 7% is equal to an eAG of 154 mg/dL. The eAG terminology can help patients better interpret the results of their A1C tests, and make it easier to correlate A1C with results from home blood glucose monitoring.
Type 1 diabetes is characterized by the presence of a variety of antibodies that attack the islet cells. These antibodies are referred to as autoantibodies because they attack the body's own cells -- not a foreign invader. Blood tests for these autoantibodies can help differentiate between type 1 and type 2 diabetes.
Screening Tests for Complications
Screening Tests for Heart Disease. All patients with diabetes should be tested for high blood pressure (hypertension) and unhealthy cholesterol and lipid levels and given an electrocardiogram. Other tests may be needed in patients with signs of heart disease.
Click the icon to see an image of an ECG.
Screening Tests for Kidney Damage. The earliest manifestation of kidney disease is microalbuminuria, in which tiny amounts of a protein called albumin are found in the urine. Microalbuminuria is also a marker for other complications involving blood vessel abnormalities, including heart attack and stroke.
People with diabetes should have an annual microalbuminuria urine test. Patients should also have their blood creatinine tested at least once a year. Creatinine is a waste product that is removed from the blood by the kidneys. High levels of creatinine may indicate kidney damage. A doctor uses the results from a creatinine blood test to calculate the glomerular filtration rate (GFR). The GFR is an indicator of kidney function; it estimates how well the kidneys are cleaning the blood.
Screening for Retinopathy. The American Diabetes Association recommends that patients with type 1 diabetes have an annual comprehensive eye exam, with dilation, to check for signs of retina disease (retinopathy). Patients at low risk may need exams only every 2 - 3 years. In addition to a comprehensive eye exam, fundus photography may be used as a screening tool. Fundus photography uses a special type of camera to take images of the back of the eye.
Screening for Neuropathy. All patients should be screened for nerve damage (neuropathy), including a comprehensive foot exam. Patients who lose sensation in their feet should have a foot exam every 3 - 6 months to check for ulcers or infections.
Screening for Thyroid Abnormalities. Thyroid function tests should be performed.