Diagnosis of Diabetes
How Are Diabetes and Prediabetes Diagnosed?
The following tests are used for the diagnosis of diabetes:
- A fasting plasma glucose test measures your blood glucose after you have gone at least 8 hours without eating. This test is used to detect diabetes or prediabetes.
- An oral glucose tolerance test measures your blood sugar after you have gone at least eight hours without eating and two hours after you drink a glucose-containing beverage. This test can be used to diagnose diabetes or prediabetes.
- In a random plasma glucose test, your doctor checks your blood sugar without regard to when you ate your last meal. This test, along with an assessment of symptoms, is used to diagnose diabetes but not pre-diabetes.
Positive test results should be confirmed by repeating the fasting plasma glucose test or the oral glucose tolerance test on a different day.
Fasting Plasma Glucose (FPG) Test
The FPG is the preferred test for diagnosing diabetes and is most reliable when done in the morning. Results and their meaning are shown in table 1. If your fasting glucose level is 100 to 125 mg/dL, you have a form of prediabetes called impaired fasting glucose (IFG), meaning that you are more likely to develop type 2 diabetes but do not have it yet. A level of 126 mg/dL or above, confirmed by repeating the test on another day, means that you have diabetes.
Table 1. Fasting Plasma Glucose Test
| Plasma Glucose Result (mg/dL) | Diagnosis |
| 99 and below | Normal |
| 100 to 125 | Prediabetes (impaired fasting glucose) |
| 126 and above | Diabetes* |
*Confirmed by repeating the test on a different day.
Oral Glucose Tolerance Test (OGTT)
Research has shown that the OGTT is more sensitive than the FPG test for diagnosing prediabetes, but it is less convenient to administer. The OGTT requires you to fast for at least eight hours before the test. Your plasma glucose is measured immediately before and two hours after you drink a liquid containing 75 grams of glucose dissolved in water. Results and what they mean are shown in table 2. If your blood sugar level is between 140 and 199 mg/dL 2 hours after drinking the liquid, you have a form of prediabetes called impaired glucose tolerance or IGT, meaning that you are more likely to develop type 2 diabetes but do not have it yet. A two-hour glucose level of 200 mg/dL or above, confirmed by repeating the test on another day, means that you have diabetes.
Table 2. Oral Glucose Tolerance Test
| 2-Hour Plasma Glucose Result (mg/dL) | Diagnosis |
| 139 and below | Normal |
| 140 to 199 | Prediabetes (impaired glucose tolerance) |
| 200 and above | Diabetes* |
*Confirmed by repeating the test on a different day.
Gestational diabetes is also diagnosed based on plasma glucose values measured during the OGTT. Blood sugar levels are checked four times during the test. If your blood sugar levels are above normal at least twice during the test, you have gestational diabetes. Table 3 shows the above-normal results for the OGTT for gestational diabetes.
Table 3. Gestational Diabetes: Above-Normal Results for the Oral Glucose Tolerance Test
| When | Plasma Glucose Result (mg/dL) |
| Fasting | 95 or higher |
| At 1 hour | 180 or higher |
| At 2 hours | 155 or higher |
| At 3 hours | 140 or higher |
Note: Some laboratories use other numbers for this test.
For additional information about the diagnosis and treatment of gestational diabetes, see the NIDDK booklet What I Need to Know About Gestational Diabetes.
WebMD Medical Reference
1
2
3
4
5
6
Is This Normal?
Get the Facts Fast!Answer:
Your level is currently NormalHigh (hyperglycemia).Low (hypoglycemia). |
If the level is below 70 and you are experiencing symptoms such as shaking, sweating or difficulty thinking, you will need to raise the number immediately. A quick solution is to eat a few pieces of hard candy or 1 tablespoon of sugar or honey. Recheck your numbers again in 15 minutes to see if the number has gone up. If not, repeat the steps above or call your doctor.
People who experience hypoglycemia several times in a week should call their health care provider. It's important to monitor your levels each day so you can make sure your numbers are within the range. If you are pregnant always consult with your health care provider.
If the level is below 70 and you are experiencing symptoms such as shaking, sweating or difficulty thinking, you will need to raise the number immediately. A quick solution is to eat a few pieces of hard candy or 1 tablespoon of sugar or honey. Recheck your numbers again in 15 minutes to see if the number has gone up. If not, repeat the steps above or call your doctor.
People who experience hypoglycemia several times in a week should call their health care provider. It's important to monitor your levels each day so you can make sure your numbers are within the range. If you are pregnant always consult with your health care provider.
Your blood sugar level is slightly high. You should call your health care provider and ask if laboratory tests to check for diabetes are needed. If you are pregnant always consult with your health care provider.
Congratulations on taking steps to manage your health.
However, it's important to continue to track your numbers so that you can make lifestyle changes if needed. If you are pregnant always consult with your physician.
Your level is currently normal. However, if you are concerned about diabetes speak with your physician. There may be other risk factors that increase your risk for diabetes.
Your level is high if this reading was taken before eating. Aim for 70-130 before meals and less than 180 two hours after meals.
Even if your number is high, it's not too late for you to take control of your health and lower your blood sugar.
One of the first steps is to monitor your levels each day. If you are pregnant always consult with your physician.
Your blood sugar level may be high, depending on when you last ate. If you have not eaten for at least 8 hours, your blood sugar should be less than 100. If you've eaten within the last 2 hours, your blood sugar should be less than 140. You should call your health care provider and ask if you need laboratory tests to check for diabetes. If you are pregnant always consult with your health care provider.
Blood sugars consistently above 180 warrant prompt medical attention.
Even if your number is high, it's not too late for you to take control of your health and lower your blood sugar.
One of the first steps is to monitor your levels each day. If you are pregnant always consult with your physician.
Your blood sugar level is high. You should call your health care provider and ask if laboratory tests to check for diabetes are needed. If you are pregnant always consult with your health care provider.
Become a Rite Aid wellness+ for diabetes member and get:
- Diet tips and fitness ideas
- Tools and trackers to help monitor your blood sugar and more
- Special offers and money-saving coupons
This tool is not intended for women who are pregnant.
