Diabetes is characterized by abnormally elevated blood glucose levels over a period of time. Insulin is either produced in too low amount (Type 1) or not used properly (Type 2). Insulin is the principle hormone that helps the cells take up glucose. Since the amount is higher than normal, it’s possible to take different tests that detect them.
One of the standard tests is called a ‘Fasting Plasma Glucose’ (FPG) test. The patient foregos eating for at least 8 hours (usually nothing after midnight). The test is administered by drawing blood and measuring the results. A normal fasting glucose level will be lower than about 99 mg/dL.
Levels between 100-125 mg/dL are an indication of a condition professionals call ‘pre-diabetes’. In this case, the person doesn’t have diabetes but is very likely to develop it within a few years unless management of glucose levels is undertaken by diet, exercise and possibly medication.
A level of 126 mg/dL or higher is a very strong indicator of full blown diabetes. When it’s seen doctors will typically recommend other tests to aid in confirming the diagnosis. One of those is called an ‘Oral Glucose Tolerance Test’ (OGTT).
A patient who has fasted drinks a high glucose liquid (75 grams, not tasty but not harmful) and blood is drawn to test. The glucose levels are measured, then the test is repeated at intervals, usually two hours later, then three, then four. Sometimes the test interval is 30 min, 1 hour, 2 hours and so on.
A 2-hour glucose level of 139 mg/dL or below is considered normal. Insulin is released by the body in reaction to the high glucose and the cells take it up. But when the number is still 140-199 mg/dL two hours later, this is an indication that inadequate insulin is released or its normal action is being hindered. That suggests pre-diabetes. When the number is 200 mg/dL or higher, diabetes is indicated.
In the latter case, physicians will often recommend repeating the test at a later date to confirm the diagnosis. Many things can temporarily alter the body’s blood glucose levels and its ability to regulate them. For example, taking steroids significantly alters blood glucose levels, as do certain diuretics. Pregnancy is one common example of a condition affecting glucose levels.
Another type of diabetes, one that occurs in about 3% of pregnancies (usually during 24-28 weeks gestation), is known as gestational diabetes. The OGTT is used to detect that as well. The test will be administered four times and the blood glucose level measured at each instance.
Another test commonly used is called the ‘Random Plasma Glucose’ (RPG) test. In this case a blood test is done without fasting. When the level is 200 mg/dL or higher it can indicate the presence of diabetes. Common symptoms are taken into account as well, such as unusually frequent urination, abnormal continued thirst even after drinking water and others.
No single test conclusively proves that a person has diabetes. Since the condition is potentially serious, though often managed with minimal lifestyle interruption, a battery of tests should be used before reaching a confirmed diagnosis.