The amount of glucose in your blood will vary depending on what and when you eat. However, in spite of these variances, the range should be relatively narrow. Generally, your blood sugar will be highest right after you eat, and lowest when you have not eaten for 8-10 hours. Most persons, after fasting all night, will have blood glucose level readings between 70 and 110 milligrams of glucose per deciliter of blood (mg/dL). After eating a large meal, it is normal for a person's blood sugar to rise. Generally, this increase will not be above 140 mg/dL. People with diabetes that is untreated will have higher blood sugars than normal both after fasting, and after eating.

When giving you a diabetes test, your doctor will determine your blood sugar levels. The results of these diabetes tests, along with other clinical findings, will be used to determine if you have diabetes, and if so, what type. Your doctor will not be able to make a definite diagnosis of diabetes on the basis of one single test. Instead, two or more glucose tests will be taken before confirming your diagnosis.

The most common diabetes tests to measure glucose are the fasting plasma glucose test, the random blood sugar test, and the oral glucose tolerance test.

Fasting Plasma Glucose Test - A fasting plasma glucose test to diagnose diabetes is the test most experts recommend using. Prior to taking this test, you are not allowed to eat anything for 8 to 10 hours. Your doctor will draw blood from a vein in your arm, and send it to a laboratory for testing. Should the test results show your fasting blood glucose to be 126 mg/dL or higher, your doctor will probably diagnose you with diabetes.

Random Blood Sugar Test - It is not uncommon for many cases of diabetes to be found during routine physical exams when your blood has been drawn for other tests. It is likely that you did not have to fast before these physical exams, though you may have just eaten, and as a result your blood sugar may be high. Even so, your blood sugar shouldn't be higher than 200 mg/dL. If your random blood glucose test comes back higher than 200 mg/dL, your doctor will probably suspect diabetes, and may want you to take a fasting plasma glucose test.

Oral Glucose Tolerance Test - For this diabetes test, a person will consume a drink containing glucose dissolved in water. The persons blood will then be drawn in timed intervals over a three-hour period. Should the plasma glucose levels rise more than expected, the person will be diagnosed with diabetes. This test for diabetes is often used when checking pregnant women for gestational diabetes. Because it is a time-consuming, cumbersome test, it is rarely used to diagnose diabetes in other patients.

It is only after thorough diabetes testing that a conclusive diagnoses can be made. Should you find out that you do have diabetes, chances are that your condition can be successfully managed with a combination of medication, and dietary lifestyle changes.