Question:
I would like to know the specifics of the glucose tolerance test so I can
simulate the test at home with my meter. I am just curious as to my response
now before I get a test at my physical in September.
Either tell me what I can do to simulate it at home or answer the questions
below:
Is it a fasting first test?
How much glucose are we talking about in how much liquid? A previous post
said 75 g of carbs. If it is 75 carbs, could I just drink a 20 oz coke or
orange juice to minic the same input?
How soon after the drink do you test again? 30 minutes, an hour, ...?
How soon again should your glucose level drop back to normal range?
What are the ranges for good and bad in this test?
Answer:
The two primary tests and their results
which combine to make the diagnosis of diabetes
In diagnosing diabetes, physicians primarily depend upon the results of
specific glucose tests. However, test results are just part of the
information that goes into the diagnosis of diabetes. Doctors also take
into account your physical exam, presence or absence of symptoms, and
medical history. Some people who are significantly ill will have transient
problems with elevated blood sugars which will then return to normal after
the illness has resolved. Also, some medications may alter your blood
glucose levels (most commonly steroids and certain diuretics (water
pills)). The two main tests used to measure the presence of blood sugar
problems are [1] the direct measurement of glucose levels in the blood
during an overnight fast, and [2] measurement of the body's ability to
appropriately handle the excess sugar presented after drinking a high
glucose drink.
[1] Fasting Blood Glucose (Blood Sugar) Level:
The "gold standard" for diagnosing diabetes is an elevated blood sugar
level after an overnight fast (not eating anything after midnight). A value
above 140 mg/dl on at least two occasions typically means a person has
diabetes. Normal people have fasting sugar levels that generally run
between 70-110 mg/dl.
[2] The Oral Glucose Tolerance Test
An oral glucose tolerance test is one that can be performed in a doctor's
office or a lab. The person being tested starts the test in a fasting state
(having no food or drink except water for at least 10 hours but not greater
than 16 hours). An initial blood sugar is drawn and then the person is
given a "glucola" bottle with a high amount of sugar in it (75 grams of
glucose), (or 100 grams for pregnant women). The person then has their
blood tested again 30 minutes, 1 hour, 2 hours and 3 hours after drinking
the high glucose drink.
For the test to give reliable results, you must be in good health (not have
any other illnesses, not even a cold). Also, you should be normally active
(for example, not lying down or confined to a bed like a patient in a
hospital) and taking no medicines that could affect your blood glucose. The
morning of the test, you should not smoke or drink coffee. During the test,
you need to lie or sit quietly.
The oral glucose tolerance test is conducted by measuring blood glucose
levels five times over a period of 3 hours. In a person without diabetes,
the glucose levels in the blood rise following drinking the glucose drink,
but then then fall quickly back to normal (because insulin is produced in
response to the glucose, and the insulin has a normal effect of lowing
blood glucose.) In a diabetic, glucose levels rise higher than normal
after drinking the glucose drink and come down to normal levels much slower
(insulin is either not produced, or it is produced but the cells of the
body do not respond to it) (see details on type 1 and type 2 diabetes for
more information on this topic).
As with fasting or random blood glucose tests, a markedly abnormal oral
glucose tolerance test is diagnostic of diabetes. However, blood glucose
measurements during the oral glucose tolerance test can vary somewhat. For
this reason, if the test shows that you have mildly elevated blood glucose
levels, the doctor may run the test again to make sure the diagnosis is
correct.
Glucose tolerance tests may lead to one of the following diagnoses:
Normal Response
A person is said to have a normal response when the 2-hour glucose level is
less than or equal to 110 mg/dl.
Impaired Fasting Glucose
When a person has a fasting glucose equal to or greater than 110 and less
than 126 mg/dl, they are said to have impaired fasting glucose. This is
considered a risk factor for future diabetes, and will likely trigger
another test in the future, but by itself, does not make the diagnosis of
diabetes.
Impaired Glucose Tolerance
A person is said to have impaired glucose tolerance when the 2-hour glucose
results from the oral glucose tolerance test are greater than or equal to
140 but less than 200 mg/dl. This is also considered a risk factor for
future diabetes. There has recently been discussion about lowering the
upper value to 180 mg/dl to diagnose more mild diabetes to allow earlier
intervention and hopefully prevention of diabetic complications.
Diabetes
A person has diabetes when oral glucose tolerance tests show that the blood
glucose level at 2 hours is equal to or more than 200 mg/dl. This must be
confirmed by a second test (any of the three) on another day. There has
recently been discussion about lowering the upper value to 180 mg/dl to
diagnose more people with mild diabetes to allow earlier intervention and
hopefully prevention of diabetic complications.
Gestational Diabetes
A woman has gestational diabetes when she is pregnant and has any two of
the following: a fasting plasma glucose of more than 105 mg/dl, a 1-hour
glucose level of more than 190 mg/dl, a 2-hour glucose level of more than
165 mg/dl, or a 3-hour glucose level of more than 145 mg/dl.
