Laboratory Tests for Diabetes
Many of the tests you have done at the laboratory
can help you to understand where things are at with
your diabetes. They can also help you see changes
over time and whether the strategies you are using
in your diabetes management are working or not.
Laboratories in New Zealand operate under strict
quality control. This means that the tests you have
done at the laboratory are likely to be very
reliable and accurate.
start of this article deals with the tests you may
have done to find out if you have diabetes. If you
already know you have diabetes, go to the section:
"What tests do I have to find out how my diabetes
management is going?".
What Tests Can be Done to Find Out if I Have
There are a number of tests that
may be done to find out if you have diabetes.
fasting blood glucose level is a measure of how much
glucose is in your blood when you have not eaten
anything for the past eight to ten hours.
test is normally taken first thing in the morning.
Your doctor or nurse will ask you to have nothing to
eat after you go to bed at night. When you wake up
in the morning you visit the laboratory for the test
before you have had anything to eat or drink (except
fasting blood glucose level of either 7mmol/L or
greater tells you that you have diabetes. If you
have no symptoms of diabetes (thirst, tiredness,
repeated infections and needing to pass urine often)
the test should be repeated on another day.
Fasting blood glucose level is now the recommended
test for finding out if you have diabetes.
fasting blood glucose level can tell you other
things as well. If your fasting blood glucose level
is between 6.1mmol/L and 6.9mmol/L you may have a
condition called "impaired fasting glycaemia" (IFG)
or pre-diabetes. This means that the level of
glucose in your blood after eating nothing overnight
is higher than it is in people without pre-diabetes
or IFG, but not as high as it is in people who have
Most doctors will ask you to have a test called an
"Oral Glucose Tolerance Test" (OGTT) if your fasting
blood glucose shows that you have IFG. The oral
glucose tolerance test may show that you actually
have diabetes or "impaired glucose tolerance" (IGT)
instead of IFG.
your tests show that you have either IFG or IGT you
need to take action to manage these conditions.
Having either of these conditions means you are more
likely to go on to develop diabetes. You are also at
higher risk of developing cardiovascular disease,
that is, disease of your heart and blood vessels.
Have IFG or IGT you Should:
Organise to be checked once a
year for diabetes (and at any time that you have
the symptoms of diabetes). Ask your doctor to put
you on an annual recall for this test. Or remember
to have it done at a time of the year you will
remember, eg: in the New Year or in the month of
Make sure you eat in a healthy
Keep your weight in a healthy
Have your cholesterol checked
Have your blood pressure
Have 20 - 30 minutes of
moderate exercise on most days of the week.
Glucose Tolerance Test (OGTT)
oral glucose tolerance test is a test where you go
to the laboratory before eating anything in the
morning. A blood glucose level is taken. Then you
will be asked to drink a glass of fluid containing
75 grams of glucose (this is a lot!). You stay in
the laboratory and another blood glucose level is
taken at one hour and two hours after the drink.
These blood glucose levels tell you how well your
body uses and stores the glucose you have taken in
will normally be asked to do an OGTT if your doctor
is unsure whether you have diabetes or not. This is
normally if your fasting blood glucose is less than
7mmol/L but more than 6.1mmol/L.
will also sometimes be asked to do an OGTT when you
are pregnant. All pregnant women in New Zealand are
asked to have a "glucose challenge" test when they
are 28 weeks pregnant. A glucose challenge test is
exactly the same as an OGTT except the amount of
glucose you are asked to drink is 50 grams not 75
grams. If the results of this test show your body is
not using glucose in the normal way you are asked to
go on and do a full OGTT.
OGTT is how diabetes of pregnancy (gestational
diabetes) is usually diagnosed in New Zealand.
Preparing for an OGTT
OGTT may not be accurate if you have either eaten a
very low carbohydrate diet or been having very
strenuous exercise in the three days before taking
the test. If you are doing either of these things
talk to your doctor before having an OGTT.
most accurate results of an OGTT will be achieved if
it is done after you have had a diet with normal
amounts of carbohydrate and moderate exercise only
over the previous three days.
What Do the
Results of an OGTT Mean?
you are not pregnant and your blood glucose two
hours after an OGTT is 11.1mmol/L or more you have
you are having a glucose tolerance test to see
whether you have diabetes of pregnancy (gestational
diabetes), and your blood glucose two hours after
the glucose drink is 9mmol/L or more than this, you
have diabetes of pregnancy (gestational diabetes).
Random Blood Glucose
If you have the symptoms of
diabetes you may be asked to go to the laboratory
for a random blood glucose test. This is a blood
glucose level taken at any time of the day after you
have eaten at any time (i.e. not in a fasting
state). If this level is 11.1mmol/L or more, you
Cell Antibody Tests
Many people with Type 1 diabetes
have antibodies in their blood that show the
autoimmune process that results in Type 1 diabetes.
If you have a direct relative (parent, sibling or
child) with Type 1 diabetes you can have this test
done. If you have these antibodies it's extremely
likely that you will develop Type 1 diabetes.
Blood (or Plasma)
This measures how much glucose you have in your
blood at the time the test is taken. A person
without diabetes would nearly always have a blood
glucose level somewhere between 4 and 7.5 mmol (a
'normal' blood glucose level).
This is a series of three tests
for blood glucose levels. There are different ways
of doing this kind of test but a common way is as
Have your normal breakfast and medication or
insulin. Have your normal mid-morning snack (if you
have one) and go to the laboratory for the first
blood glucose test before your lunch. Have your
usual lunch (and medication or insulin if you take
it), then go back to the laboratory 2 hours after
lunch and have your second blood glucose test taken.
Have your normal food and medication or insulin for
the rest of the day.
Have no insulin, medication or food when you wake up
in the morning. Go to the laboratory as soon as you
can and have your third blood glucose test taken.
Once this is done have your medication or insulin
and your breakfast. Your blood glucose series is now
The aim of such a series is to
get a 'picture' of your usual blood glucose levels
on a close to normal day.
Healthy Levels for a
Blood Glucose Series?
Everybody will have different
target levels depending on lots of individual
factors. You and your doctor need to work out what
are realistic and safe target levels for you.
A general guide to target levels
for a blood glucose series is:
Pre-lunch between 4.5 and 7.8mmol
hours after lunch between 4.5 and 8.5mmol
First thing in the morning(fasting) between 4 and
HBA1c level (also
Called Glycosylated HaemaglobinLevel)
This measures your average blood
glucose over the past 4 - 6 weeks. It measures how
much glucose is stuck onto your red blood cells. Red
blood cells have a life span of about 6 weeks and so
the test gives a good indication of what your
overall blood glucose levels have been through that
Most diabetes specialists and GPs
have a lot of confidence in this test and will use
it to help show you how you are going with your
blood glucose management.
HBA1c levels are measured as a
percentage. The HBA1c level is not directly
equivalent to blood glucose levels. For example, an
HBA1c level of 13% means that your average blood
glucose for the past 6 weeks has been around 18 - 19
Healthy HBA1c Levels?
Once again, target HBA1c levels will vary from
person to person. Work out a safe target HBA1c for
you with your doctor.
general range for HBA1c levels is:
Less than or equal to 7% is a
very healthy HBA1c level
Between 7% and 8% is a fair
HBA1c level and needs work to improve
Between 8% and 10% indicates
your blood glucose levels are much too high
Above 10% indicates your blood
glucose levels are extremely high.
If you are taking insulin and your HBA1c level
is less than 6.2% this almost certainly indicates
that you are having lots of low blood glucose
levels. Having HBA1c levels this low is not safe
when you are taking insulin.
This measures your average blood
glucose levels over the previous 2 weeks. This
measure is not as commonly used in New Zealand as
HBA1c levels. This is because many people feel HBA1c
levels tend to be more accurate and reliable.
Some diabetes services use
fructosamine as a useful measure for women who are
Because insulin needs (and
consequently blood glucose levels) change so rapidly
during pregnancy, some services prefer to use
fructosamine rather than HBA1c as it looks back over
a shorter time and therefore may reflect rapid
changes more effectively.
What is a
Healthy Fructosamine Level?
If you are not pregnant, the
target healthy level is less than 300. When you are
pregnant, the target healthy level is less than 200.
What laboratory tests are done to measure my blood
fats (cholesterol or lipid levels)?
The level of cholesterol or fats
in your blood is measured by a test called a blood
lipid profile. This measures the level of a number
of different fats in your blood.
fats that are measured are:
What Other Lab Tests am I
to Have Done?
HDL cholesterol (high density
LDL cholesterol (low density
Healthy levels of these fats are:
Total cholesterol less than or equal to 5.0mmol
HDL cholesterol greater than 1.0mmol
LDL cholesterol less than 2.5mmol
Triglycerides less than 2.0mmol.
A test you will have done
regularly (it should be done at least once a year)
is your 'microalbuminuria' level. This is a
laboratory test that is done on a sample of urine.
It involves checking for microscopic amounts of
protein in your urine.
Small amounts of protein leaking
out into your urine is an early sign that your
kidneys are developing damage from your diabetes
(diabetic nephropathy). The amount of protein
leaking into your urine can tell if you have kidney
damage and also if it is getting worse or not.
Your microalbuminuria levels
should be plotted on a graph over time. Hopefully,
these levels will stay low, but if they are rising
then this shows there is a problem happening with
your kidneys. It is best if your microalbuminuria
levels are less than 2.
If your test comes back with
raised microscopic protein levels your doctor may
ask for you to have the test again. This is because,
sometimes, your microalbuminuria levels can be up if
you have an infection or even if you have been
exercising hard. If they are up for this reason this
is just temporary and not a problem. Repeating the
test helps to eliminate a 'false positive' for
either of these reasons.
You may also have your thyroid
hormone levels tested (especially if you have Type 1
Checking your thyroid function
involves having a sample of blood taken at the
laboratory. Some diabetes clinics will check your
thyroid function on a fairly regular basis. Your
doctor will discuss the results with you.
A lipids test measures the level
of fats (lipids) in your blood. A rising level of
certain blood fats can alert your doctor to an
increased risk of blood vessel damage. The test
measures the level of two such substances, which
increase your heart disease risk: low-density
lipoprotein (LDL), the "bad" cholesterol, and
triglycerides. The test also determines your level
of high-density lipoprotein (HDL), the "good"
cholesterol, which protects against heart disease.
The Test is Done?
A lab technician takes a sample
of blood from a vein in your arm and sends the blood
sample to a lab for analysis.
Optimal levels are:
How Often to Have the
LDL: Less than 100 milligrams per deciliter (mg/dL)
HDL: Greater than 40 mg/dL if you're a man or
greater than 50 mg/dL if you're a woman
Triglycerides: Less than 150 mg/dL
The ADA recommends that you have
this test at least once each year and more often if
your levels aren't normal or you're taking