Overview & Description
Blood glucose, also called blood sugar, is the amount of glucose circulating
in the blood. Glucose is a type of sugar. The body forms glucose when it breaks
foods that a person eats down into a useable form of energy. Glucose is a main
energy source for the body.
Measuring the amount of blood glucose in the blood helps evaluate:
how the body is converting and breaking foods down into energy
how the liver is working
how the organs in the body that help regulate blood glucose are working
Blood glucose can be measured in a number of ways. Some of the
tests that can measure blood glucose include:
fasting blood glucose test
glycosylated hemoglobin,
also called HbA1c or hemoglobin A1c test
oral glucose tolerance test
random blood glucose test
self-monitoring of blood glucose, also called SMBG, or home
blood glucose monitoring
tests
Who is a candidate for the test?
A doctor may order a blood glucose test to evaluate
the amount of glucose in the blood when he or she suspects a person has
diabetes.
These tests may also be done to rule out other causes of high or low blood glucose.
How is the test performed?
Here's how some of the tests may be done to check blood glucose
levels:
A fasting blood glucose test is the preferred method to diagnose
diabetes
and rule out other conditions. This test is done after a person has had nothing to
eat or drink except water for at least 8 hours. This is often called fasting. It is
generally started overnight so the test can be done in the morning. Normal fasting
plasma glucose levels are less than 110 mg/dL (milligrams per deciliter). Fasting plasma glucose levels of
more than 126 mg/dL on two or more tests done on different days usually indicate
diabetes.
Levels between 110 and 126 indicate a condition known as pre-diabetes.
An HbA1c, also known as glycosylated hemoglobin,
measures the average blood glucose over the past 3 months. It is a good
measure of long-term blood glucose control. This test is generally done only in
people who have diabetes. It is used to assess how well their therapy is working.
An oral glucose tolerance test requires a person to drink a premeasured amount of a
glucose drink. Then two hours later, a blood glucose measurement is done. Healthy
glucose levels with this test are less than 140 mg/dL. If the blood glucose is
greater than 200 mg/dL, then another test is done on a different day to confirm whether
the person has diabetes
or not. Usually the fasting blood glucose test or the random glucose test is done.
A random blood glucose test is done shortly after a person has eaten
or had something to drink. A level of 200 mg/dL or higher
may indicate diabetes.
Usually if a level is above 200 mg/dL, a fasting glucose test or oral
glucose tolerance test
is done to confirm the diagnosis of diabetes.
A self-monitoring of blood glucose, also called SMBG or home blood glucose monitoring,
lets a person monitor blood glucose at home. This is done only by people who have
diabetes.
A record of daily blood glucose readings can be kept to follow changes in glucose
levels throughout the day. This can be useful to the doctor in deciding if changes need to
be made to the person's diabetes treatment plan.
For most blood glucose tests, a blood sample is taken from a vein in
the arm. First, the skin over the vein is cleaned with an antiseptic. A thin strip
of rubber called a tourniquet is wrapped around the upper arm to enlarge the veins.
A small needle is gently inserted into the enlarged vein. Then blood is collected
for testing in the laboratory. After the tourniquet is removed, a cotton ball is held
over the needle site until bleeding stops. The laboratory then tests the blood
sample.
The home blood glucose monitoring
system, on the other hand, uses a small drop of blood from a person's finger.
The drop is put onto a special strip of paper, which is then inserted into the
blood glucose monitor machine. The monitor measures and displays the blood
glucose reading. This test can monitor blood glucose fairly accurately if the person
follows the directions carefully.
Results and Values
What do the test results mean?
The normal blood glucose levels also vary depending on:
which test was performed
whether a person was fasting before the test
whether any special dietary or glucose substances were given during testing
Increased levels of blood glucose, a condition known as
hyperglycemia, may be caused by the following:
acromegaly,
a condition that causes elongation of the bones of the limbs and head
Cushing syndrome,
a condition in which the level of the hormone cortisol is too high and causes
fatigue,
weakness,
protein loss, swelling, and diabetes mellitus, which is also called DM
diabetes mellitus
diuretics, also known as water pills
gestational diabetes,
or diabetes that develops during pregnancy
inadequate therapy for diabetes mellitus
infection in the pancreas, known as pancreatitis
kidney failure, such as chronic renal failure
liver disease,
such as cirrhosis
pheochromocytoma,
which is a noncancerous tumor that causes an increase in certain chemicals
that can cause high blood pressure
steroid medicines, such as prednisone
stress
response, including infection, severe burns,
or surgery
Decreased levels of blood glucose, a condition known as
hypoglycemia,
may be caused by the following:
Addison disease,
a condition in which there is a decreased amount of the adrenocorticol hormone
blood loss
extensive liver disease
hypopituitarism, a condition in which the pituitary gland does not release enough hormone
hypothyroidism,
a condition in which too little thyroid hormone is present in the blood
insulin overdose
insulinoma, which is a tumor in the pancreas that causes too much insulin to be produced
malabsorption,
or inadequate absorption of nutrients from the stomach or intestines
starvation
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