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Reviewed by Professor Ian W Campbell, consultant physician
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What is the blood sugar level?
The blood sugar level is the amount of glucose (sugar) in the
blood. It is also known as plasma glucose level. It is expressed as millimoles
per litre (mmol/l).
Normally blood glucose levels stay within narrow limits
throughout the day: 4 to 8mmol/l. But they are higher after meals and usually
lowest in the morning.
In
diabetes the blood
sugar level moves outside these limits until treated. Even with good control of
diabetes, the blood sugar level will still at times drift outside this normal
range.
Why control blood sugar levels?
When very high levels of blood glucose are present for years,
it leads to damage of the small blood vessels.
This in turn increases your risk of developing late-stage
diabetes complications including:
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retinopathy (eye
disease)
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nephropathy (kidney
disease)
-
neuropathy (nerve
disease)
-
cardiovascular
disease, such as
heart attack,
hypertension,
heart failure,
stroke and problems
caused by poor circulation, eg gangrene in the worst cases.
With
Type 1 diabetes,
these complications may start to appear 10 to 15 years after
diagnosis.
They frequently appear less than 10 years after diagnosis of
Type 2 diabetes,
because this type of diabetes is often present for years before it is
recognised.
By keeping the blood sugar level stable, you significantly
reduce your risk of these complications.
How can I measure blood sugar levels?
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Good advice
Home testing kits come in a variety of shapes and
sizes.
A pharmacist or the diabetes clinic nurse can advise you about
the best model.
You can usually obtain a blood glucose meter at little or no
cost via the diabetes clinic.
Testing strips are available on NHS prescription.
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You can learn to measure blood sugar levels simply and quickly
with a home blood glucose level testing kit. All kits have at least two things:
a measuring device and a strip.
To check your blood sugar level, put a small amount of blood on
the strip. Now place the strip into the device. After about 30 seconds it will
display the blood glucose level.
The best way to take a blood sample is by pricking your finger
with a sharp lancet that's designed to penetrate the skin only as far as needed
to draw a drop of blood.
What should glucose levels be?
The ideal values are:
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4 to 7mmol/l before meals
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less than 10mmol/l 90 minutes after a meal
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around 8mmol/l at bedtime.
How often should blood glucose levels be measured?
It depends on your lifestyle - the needs of someone with
diabetes who's also a PE instructor are quite different to someone who sits at
a computer all day.
If you use insulin
In broad terms, people who have Type 1 diabetes should
measure their blood sugar levels daily before meals. Some days one or two tests
can be done, while on others four or five might be needed.
Measuring blood sugar levels in the morning before any food
gives an indication of the amount of
insulin needed
overnight.
If you have Type 2 diabetes that's being treated with insulin,
you should also follow this schedule.
If you take oral treatments
If your diabetes is treated with
tablets or a special diet (Type 2),
you should measure your blood glucose levels once or twice a week - either
before meals or 90 minutes after a meal.
You should also do a 24-hour profile once or twice a month.
This means measuring glucose levels before each meal.
Not everyone with Type 2 diabetes needs to carry out regular
blood glucose checks.
For elderly people and those with other medical problems,
it's often enough to check the urine for glucose - usually before breakfast and
the evening meal.
This is because while good control of diabetes is important,
cardiovascular complications (heart attacks, stroke,
angina) are the main
cause of serious illness and death in people with this type of
diabetes.
So people with Type 2 diabetes will benefit from tackling the
factors that contribute to their cardiovascular risk by:
-
controlling
blood
pressure more rigorously
-
lowering cholesterol levels with
medication
-
increasing or starting exercise
-
stopping smoking.
Blood glucose levels at bedtime
The blood sugar level at bedtime should be between 7 and 10
mmol/l.
If
blood glucose is very
low or very high at bedtime, you may need to adjust your food intake or
insulin dose. Make sure you discuss this with your doctor.
At what other times should blood glucose levels be
measured?
Blood glucose should be measured any time you feel unwell or
think your blood sugar level is too high or low.
If you have Type 1 diabetes and have more than 20mmol/l of
glucose in your blood, you should use a urine strip to check for the presence
of ketones.
One of the blood glucose meters available also allows you to
check your blood for ketones.
If ketone bodies are present in your urine or blood, it's a
warning sign of
diabetic acidosis. If
this is the case, you should consult your doctor immediately.
How is the blood sugar level checked over a period of
time?
A test known as the HbA1c test can show the average blood sugar
level over the previous six to eight weeks.
The test looks at levels of HbA1c in a
sample of
blood.
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Term watch
Haemoglobin
The substance in red blood cells that binds to oxygen and
transports it around the bloodstream.
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HbA1c is the compound produced by the chemical reaction between
haemoglobin and glucose in the blood. HbA1c is also called glycated
haemoglobin.
High blood sugar levels produce more HbA1c. But because the
process happens over several weeks, an occasional blip of high blood sugar is
not enough to influence the HbA1c level.
This means only consistently high glucose levels cause HbA1c
levels to rise - and why HbA1c levels are used as a measure of diabetes
control.
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HbA1c is about 6 per cent of the total haemoglobin in people
who don't have diabetes. The target to aim for is an HbA1c level of below 6.5
per cent if possible – although 7 per cent or
less is very good.
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HbA1c of 7.5 per cent shows only fair control of
diabetes.
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HbA1c above 8.5 per cent shows poor control of
diabetes.
Any increase in the HbA1c level indicates poorer control of
diabetes.
The United Kingdom Prospective Diabetes Study Group (UKPDS) was
a 20-year-long research trial in diabetes.
It showed that for every 1 per cent rise in HbA1c, a person with
Type 2 diabetes is 30 per cent more likely to develop late-stage complications
arising from damage to the small blood vessels.
In Type 1 diabetes, the same relationship between high HbA1c and
increased development of complications was shown by the Diabetes Control and
Complications Trial in the US.
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References
Home P, Mant J, Turner C, et al. Management of Type 2 diabetes:
summary of updated NICE guidance. BMJ 2008; 336: 1306-8.
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Based on a text by Dr Jan Erik Henriksen and Dr Henning Bech-Nielsen, professor and consultant
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Last updated 09.09.2008
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