Tests Used To Diagnose Diabetes
A fasting plasma glucose test measures your blood
glucose after you have take at least 8 hours without eating or fasting. This
test is used to detect whether you have diabetes or pre-diabetes.
A fasting plasma glucose test measures your blood
glucose after you have take at least 8 hours without eating or fasting. This
test is used to detect whether you have diabetes or pre-diabetes.
An oral glucose tolerance test measures your blood
glucose in two conditions. The first one is after you have take at least 8
hours of fasting followed by another test 2 hours after you drink a
glucose-containing beverage. This test can be used to diagnose diabetes or
pre-diabetes.
In a random plasma glucose test, your doctor checks your
blood glucose 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 due to
convenience 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 pre-diabetes 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.
Oral Glucose Tolerance Test (OGTT)
Research has shown that the OGTT is more sensitive than the
FPG test to diagnose pre-diabetes, but it is less convenient to administer. The
OGTT requires you to fast for at least 8 hours before the test. Your plasma
glucose is measured immediately before and 2 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 glucose level is between 140 and 199 mg/dL 2
hours after drinking the liquid, you have a form of pre-diabetes called
impaired glucose tolerance or IGT, meaning that you are more likely to develop
type-2 diabetes but do not have it yet. A 2-hour glucose level of 200 mg/dL or
above, confirmed by repeating the test on another day, means that you have
diabetes.
Gestational diabetes is also diagnosed based on plasma
glucose values measured during the OGTT. Blood glucose levels are checked four
times during the test. If your blood glucose 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.
For additional information about
the diagnosis and treatment of gestational diabetes, see the NIDDK booklet What I
Need to Know About Gestational Diabetes.
Random Plasma Glucose Test
A random blood glucose level of 200 mg/dL or more, plus
presence of the following symptoms, can mean that you have diabetes:
- Increased urination
- Increased thirst
- Unexplained weight loss
- Other symptoms include fatigue, blurred vision, increased hunger, and sores that do not heal. Your doctor will check your blood glucose level on another day using the FPG or the OGTT to confirm the diagnosis.
Summary of diabetes diagnosis measurements can be seen in this following table:
