Diabetes is a disease in which blood glucose levels are above normal. People
with diabetes have problems converting food to energy. After a meal, food is
broken down into a sugar called glucose, which is carried by the blood to cells
throughout the body. Cells use insulin, a hormone made in the pancreas, to help
them convert blood glucose into energy.
People develop diabetes because the pancreas does not make enough insulin or
because the cells in the muscles, liver, and fat do not use insulin properly, or
both. As a result, the amount of glucose in the blood increases while the cells
are starved of energy. Over the years, high blood glucose, also called
hyperglycemia, damages nerves and blood vessels, which can lead to complications
such as heart disease and stroke, kidney disease, blindness, nerve problems, gum
infections, and amputation.
Types of Diabetes
The three main types of diabetes are type 1, type 2, and gestational
- Type 1 diabetes, formerly called juvenile diabetes, is usually first
diagnosed in children, teenagers, or young adults. In this form of diabetes, the
beta cells of the pancreas no longer make insulin because the body’s immune
system has attacked and destroyed them.
- Type 2 diabetes, formerly called adult-onset diabetes, is the most common
form. People can develop it at any age, even during childhood. This form of
diabetes usually begins with insulin resistance, a condition in which muscle,
liver, and fat cells do not use insulin properly. At first, the pancreas keeps
up with the added demand by producing more insulin. In time, however, it loses
the ability to secrete enough insulin in response to meals.
- Gestational diabetes develops in some women during the late stages of
pregnancy. Although this form of diabetes usually goes away after the baby is
born, a woman who has had it is more likely to develop type 2 diabetes later in
life. Gestational diabetes is caused by the hormones of pregnancy or by a
shortage of insulin.
Type 1 Diabetes and Type 2 Diabetes
To move away from basing the names of the two main types of diabetes on
treatment or age at onset, an American Diabetes Association expert committee
recommended in 1997 universal adoption of simplified terminology. The National
Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) agrees.
|Former Names||Preferred Names|
|type 1 diabetes|
|type 2 diabetes|
What is pre-diabetes?
In pre-diabetes, blood glucose levels are higher than normal but not high
enough to be characterized as diabetes. However, many people with pre-diabetes
develop type 2 diabetes within 10 years. Pre-diabetes also increases the risk of
heart disease and stroke. With modest weight loss and moderate physical
activity, people with pre-diabetes can delay or prevent type 2 diabetes.
How are diabetes and pre-diabetes diagnosed?
The following tests are used for diagnosis:
- 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
- An oral glucose tolerance test measures your blood glucose after you
have gone at least 8 hours without eating and 2 hours after you drink a
glucose-containing beverage. This test can be used to diagnose diabetes or
- 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
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
Table 1. Fasting Plasma Glucose Test
|Plasma Glucose Result (mg/dL)||Diagnosis|
|99 and below||Normal|
|100 to 125||Pre-diabetes
(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 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.
2. Oral Glucose Tolerance Test
|2-Hour Plasma Glucose Result (mg/dL)||Diagnosis|
|139 and below||Normal|
|140 to 199||Pre-diabetes
(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 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.
Table 3. Gestational Diabetes:
Results for the Oral Glucose Tolerance Test
|When||Plasma Glucose Result (mg/dL)|
|Fasting||95 or higher|
|At 1 h|