As diabetes is characterized by abnormal blood sugar levels due to ineffectiveness of insulin, blood sugar levels are an important parameter for the diagnosis, treatment and prognosis of diabetes. Blood glucose levels vary at different time on various part of the day. The factors on which our blood sugar levels depend are: age, intensity of physical activity, body composition, type of diet consumed and stress.
The following tests are used for diagnosis:
- A Fasting Plasma Glucose (FPG) Test:- A fasting plasma glucose (FPG) test measures blood glucose in a person who has not eaten anything for at least 8 hours. This test is used to detect diabetes and pre-diabetes. The FPG test is most reliable when done in the morning. Fasting Blood Glucose Test is convenient and has low cost. However, it sometimes misses diabetes or pre- diabetes and has to be confirmed with the OGTT. People with a fasting glucose level of 100 to 125 milligrams per deciliter (mg/dL) have a form of pre-diabetes called impaired fasting glucose (IFG). Having IFG means a person has an increased risk of developing type 2 diabetes but does not have it yet. A level of 126 mg/dL or above, confirmed by repeating the test on another day, means a person has diabetes.
| Plasma Glucose Result (mg/dL) | Diagnosis |
| 99 or below | Normal |
| 100 to 125 | Pre-diabetes (impaired fasting glucose) |
| 126 or above | Diabetes |
- Oral Glucose Tolerance Test (OGTT):- An oral glucose tolerance test (OGTT) measures blood glucose after a person fasts at least 8 hours and 2 hours after the person drinks a glucose-containing beverage. This test can be used to diagnose diabetes and pre-diabetes. Research has shown that the OGTT is more sensitive than the FPG test for diagnosing pre-diabetes, but it is less convenient to administer. The OGTT requires fasting for at least 8 hours before the test. The plasma glucose level is measured immediately before and 2 hours after a person drinks a liquid containing 75 grams of glucose dissolved in water. If the blood glucose level is between 140 and 199 mg/dL 2 hours after drinking the liquid, the person has a form of pre-diabetes called impaired glucose tolerance (IGT). Having IGT, like having IFG, means a person has an increased risk of developing type 2 diabetes but does not have it yet. A 2-hour glucose level of 200 mg/dL or above, confirmed by repeating the test on another day, means a person has diabetes.
| 2-Hour Plasma Glucose Result (mg/dL) | Diagnosis |
| 139 and below | Normal |
| 140 to 199 | Pre-diabetes (Impaired Glucose Tolerance) |
| 200 and above | Diabetes |
- Gestational Diabetes:- Gestational diabetes is also diagnosed based on plasma glucose values measured during the OGTT, preferably by using 100 grams of glucose in liquid for the test. Blood glucose levels are checked four times during the test. If blood glucose levels are above normal at least twice during the test, the woman has gestational diabetes. Following table shows the above-normal results for the OGTT for gestational diabetes.
| Gestational diabetes: Above-normal results for the OGTT | |
| 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 |
- Random Plasma Glucose Test:- A random plasma glucose test, also called a casual plasma glucose test, measures blood glucose without regard to when the person being tested last ate. This test, along with an assessment of symptoms, is used to diagnose diabetes but not pre-diabetes. Test results indicating that a person has diabetes should be confirmed with a second test on a different day. A random, or casual, blood glucose level of 200 mg/dL or higher, plus the presence of the following symptoms, can mean a person has diabetes (increased urination increased thirst unexplained weight loss).
- Other symptoms can include fatigue, blurred vision, increased hunger, and sores that do not heal. The doctor will check the person’s blood glucose level on another day using the FPG test or the OGTT to confirm the diagnosis.