Healthy adults age 45 and older should get tested for diabetes every 3 years. Patients who have certain risk factors should ask their doctors about testing at an earlier age and more frequently. These risk factors include:
- A weight that is 20% more than ideal body weight
- Sedentary lifestyle
- High blood pressure (greater than 140/90) or unhealthy cholesterol levels -- especially for patients with low HDL ("good") cholesterol and high triglyceride levels
- History of heart disease, stroke, or peripheral artery disease
- A close relative (parent, sibling) with diabetes
- A high-risk ethnic group background (African-American, Latino, Native American, Asian American, Pacific Islander)
- Having delivered a baby weighing over 9 pounds or having a history of gestational diabetes (in women)
- Polycystic ovary disease (in women)
Children age 10 and older should be tested for type 2 diabetes (even if they have no symptoms) every 3 years if they are overweight and have at least two risk factors.
Testing for Diabetes and Pre-Diabetes
Pre-diabetes precedes the onset of type 2 diabetes. People who have pre-diabetes have fasting blood glucose levels that are higher than normal, but not yet high enough to be classified as diabetes. (Pre-diabetes used to be referred to as “impaired glucose tolerance.”) Pre-diabetes greatly increases the risk for diabetes.
There are three tests that can be used to diagnose diabetes or identify pre-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 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. 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 test is normal in people who have symptoms or risk factors for diabetes.
Oral Glucose Tolerance Test
The oral glucose tolerance test (OGTT) is more complex than the FPG and may over-diagnose 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:
- The patient first has an FPG test.
- The patient has a blood test 2 hours later, after drinking a special glucose solution.
OGGT levels indicate:
- Normal. 140 mg/dL or below
- Pre-Diabetes. Between 140 - 199 mg/dL
- Diabetes. 200 mg/dL or higher
The patient cannot eat for at least 8 hours prior to the FPG and OGTT tests.
Hemoglobin A1C Test
This test examines blood levels of glycosylated hemoglobin, also known as hemoglobin A1C (HbA1c, A1c). The results are given in percentages and indicate a person’s average blood glucose levels over the past 2 - 3 months. (The FPG and OGGT 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 the blood test.
In 2010, the American Diabetes Association recommended that the test be used as another option for diagnosing diabetes and identifying pre-diabetes.
A1C levels indicate:
- Normal. Less than 5.7%
- Pre-Diabetes. Between 5.7 - 6.4%
- Diabetes. 6.5% 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 fingerprick self-testing provides information on blood glucose for that day, the A1C test shows how well blood sugar has been controlled over the period of several months. In general, most patients with diabetes should aim for A1C levels of around 7%. Your doctor may adjust this goal depending on your individual health profile.
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 to better interpret the results of their A1C tests and make it easier to correlate A1C with results from home blood glucose monitoring.
Screening Tests for Complications
Screening 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.
The electrocardiogram (ECG or EKG) is used extensively in the diagnosis of heart disease, from congenital heart disease in infants to myocardial infarction and myocarditis in adults. Several different types of electrocardiogram exist.
Screening for Kidney Damage. The earliest manifestation of kidney damage is microalbuminuria, in which tiny amounts of a protein called albumin are found in the urine. Microalbuminuria typically shows up in patients with type 2 diabetes who have high blood pressure.
The American Diabetes Association recommends that people with diabetes receive 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 cleansing the blood.
Screening for Retinopathy. The American Diabetes Association recommends that patients with type 2 diabetes get an initial comprehensive eye exam by an ophthalmologist or optometrist shortly after they are diagnosed with diabetes, and once a year thereafter. (People at low risk may need follow-up exams only every 2 - 3 years.) The eye exam should include dilation to check for signs of retinal disease (retinopathy). 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.