Blood sugar, used in a physiological context, is a misnomer and misleading. Physiologically, the term means only glucose in the blood. Other sugars are present, sometimes in more than trace amounts, but only glucose serves as a controlling signal for metabolic regulation. Other sugars are, to some extent, inert. Glucose, transported via the bloodstream from the intestines or liver to body cells, is the primary source of energy for the body's cells.
Blood sugar concentration, or glucose level, is tightly regulated in the human body. Normally, the blood glucose level is maintained between about 4 and 6 mM (mmol). The normal blood glucose level is about 90mg/100ml, which works out to 5mM/L (mmol/l), since the molecular weight of glucose, C6H12O6, is about 180 g/mol daltons. The total amount of glucose in circulating blood is therefore about 3.3 to 7g (assuming an ordinary adult blood volume of 5 liters, plausible for an average adult male). Glucose levels rise after meals for an hour or two by a few grams and are usually lowest in the morning, before the first meal of the day.
Failure to maintain blood glucose in the normal range leads to conditions of persistently high (hyperglycemia) or low (hypoglycemia) blood sugar. Diabetes mellitus, characterized by persistent hyperglycemia from any of several causes, is the most prominent disease related to failure of blood sugar regulation.
Although it is called "blood sugar," other simple sugars aside from glucose are found in the blood, such as fructose and galactose. But only glucose levels are used as metabolic regulation signals (via insulin and glucagon).
What is blood glucose level?
Blood glucose level is the amount of glucose (sugar) in the blood. It is also known as serum glucose level. The amount of glucose in the blood 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.
If a person has diabetes, their blood glucose level sometimes moves outside these limits.
Why control blood glucose levels?
When you have diabetes it's very important that your glucose level is as near normal as possible. The primary goal of any diabetes treatment is simply to keep the glucose level stable.
Stable blood glucose significantly reduces the risk of developing late-stage diabetic complications. These may start to appear 10 to 15 years after diagnosis with Type 1 diabetes and often less than 10 years after diagnosis with Type 2 diabetes. They include:
--neuropathy (nerve disease) --retinopathy (eye disease) --nephropathy (kidney disease) --cerebrovascular disease, such as stroke --cardiovascular disease, such as heart attack, hypertension and heart failure.
How can I measure blood glucose levels?
Blood glucose levels can be measured very simply and quickly with a home blood glucose level testing kit. These come in a wide variety of shapes and sizes, but they all consist of at least two things: the measuring device itself and a strip. A pharmacist will be able to advise you about the most appropriate model for you.
To check your blood glucose level put a small amount of blood on the strip and 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 the finger with a surgical knife, called a lancet.
What should glucose levels be?
The best values are:
--4 to 7mmol/l before meals. --less than 10mmol/l one-and-a-half hours after meals. --around 8mmol/l at bedtime.
How often should blood glucose levels be measured?
People who have Type 1 diabetes should measure their blood glucose level once a day, either in the morning before breakfast or at bedtime.
In addition, they should do a 24-hour profile a couple of times a week. That means measuring blood glucose levels before each meal and before bed.
People who have Type 2 diabetes and are being treated with insulin should also follow the schedule above.
People who have Type 2 diabetes and who are being treated with tablets or a special diet should measure their blood glucose levels once or twice a week either before meals or one-and-a-half hours after a meal. They should also do a 24-hour profile once or twice a month.
The main advantage for insulin-treated diabetics in measuring blood glucose levels in the morning is that appropriate amounts of insulin can be taken if the blood glucose level is high or low. This will reduce the risk of developing late-stage diabetic complications.
Blood glucose levels at bedtime
The blood glucose 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 don't feel well, or think your blood glucose is either too high or too low.
People who have Type 1 diabetes with a high level of glucose in their blood (more than 20mmol/l), in addition to sugar traces in the urine, should check for ketone bodies in their urine, using a urine strip.
If ketone bodies are present, it's a warning signal that they either have, or may develop, diabetic acidosis. If this is the case, they should consult their doctor.
What is glycated haemoglobin?
Glycated haemoglobin or HbA1c - also known as long-term glucose - shows how much of the haemoglobin in the blood is glycated. This means that a haemoglobin cell in your blood has picked up a glucose molecule. The normal amount is 6 to 7 per cent.
This test is usually done using a blood sample from the patient's arm. It shows how high the glucose levels have been over the last six to eight weeks.
Unfortunately, different hospitals have different guidelines, but generally speaking a level of:
--7 to 8 per cent is usually fine --8 to 10 per cent is not quite acceptable --above 10 per cent is unacceptable.
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