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Jan 15, 2008

The dawn phenomenon, HbA1c, and other funny terms in diabetes.

THESE are some the questions patients frequently ask me: What is HbA1c?

Why is my HbA1c high when my blood sugars are normal?

The HbA1c test is a measure of a diabetic’s blood sugar control over the preceding two to three months.
Why is my sugar level high in the morning when I am fasting and lower the rest of the day, even after food?

How do I know my diabetes is under control?

What is “good” diabetic control?

What is HbA1c?

As all the questions are inter-related. I will answer firstly by discussing about HbA1c . HbA1c , also known as glycated haemogoblin or glycosylated haemogoblin, is probably the most important test in diabetes.

The principle is simple – a protein which is part of the haemogoblin molecule is sensitive to blood sugar. High levels of blood sugar will convert it to “HbA1c””, and the higher the level of blood sugar, the greater the conversion rate.

In a normal person, the quantity of HbA1c present is 6.0% or less. Poorly controlled diabetics have an HbA1c many times higher, even up to 15%.

Good control, according to our Malaysian guidelines, is 6.5%. This is also the standard in many other countries round the world, though the Americans still stick to 7.0%.

The usefulness of this test lies in the fact that HbA1c remains essentially unchanged for six to eight weeks, so a single HbA1c reading will let your doctor know your average blood sugar readings over the preceding two to three months.

Some patients try to cheat the doctor by not adhering to a sensible diet till a week or so before they visit the doctor.

They then starve themselves over this period so that by the time they visit the clinic, their sugars are normal.

Conversely, you may have been a conscientious patient, but the week earlier your daughter got married, and the round of dinners caused your sugar levels to rocket up. But your HbA1c will remain normal and the doctor will not be concerned.

Why is the HbA1c high when my blood sugars are normal?

There are three reasons for this (excluding cheating, of course!):

1. Your test technique is faulty

2. Your machine is faulty

3. You suffer from a disease affecting your haemogoblin (haemogoblinopathy) and minor degrees of this are not uncommon in our community.

Why is my sugar level high in the morning when I am fasting and lower the rest of the day, even after food?

When you start waking up in the morning, many hormones become activated. Among them would be the growth hormone, cortisol, and adrenaline. These hormones also tend to raise the blood sugar a little.

Sometimes this response is exaggerated, and the sugars may rise significantly and then taper off the rest of the day. This is termed the Dawn Phenomenon. It is usually harmless.

Incidentally, these hormones also raise blood pressure; and if it is exaggerated, this surge in the blood pressure may result in a heart attack or stroke. This explains why heart attacks and strokes are more common in the morning.

Another reason for this is termed the “Somogyi Effect”. If you are OVERTREATED, your sugar will go down very low at night because you are not eating.

To compensate for this, the glucose stores in your liver are released and your blood sugar will suddenly rise.

In effect, this is a rebound phenomenon. The solution would be to REDUCE the dose of the medication or insulin, and not increase it.

Increasing the dose of the medication would only worsen the “Somogyi Effect”. This can be detected by checking your sugar at 3am or 4am. If it is low at this time, and high at say, 7am, then it is due to the rebound effect.

How do I know my diabetes is under control? What is ‘good’ diabetic control?

The HbA1c is the single most important parameter of diabetic control. You should aim for a HbA1c of 6.5%, or if you are elderly, perhaps 7.0% to reduce the risk of hypoglycaemia (low blood sugar level), which is more common in the elderly.

But if the HbA1c is such a good test why should the doctor ask you to check your blood sugars? Why not scrap the blood sugar test altogether?

There are several reasons why blood sugar testing is still important:

1. It helps to fine-tune diabetic control. For example, if the HbA1c is high, you want to know why. By checking your sugars regularly, you may, for example, discover that it is raised only after meals – or sometimes only after a certain type of food. You can then make the necessary adjustments to bring down the HbA1c.

Regular blood sugar monitoring and HbA1c testing every three to four months are complementary.

2. When you feel unwell suddenly, it may be because the diabetes has gone seriously out of control, for example, when you come down with an infection.

In this situation, making an early diagnosis may be life-saving. Blood sugar testing is also the only way to detect a hypoglycaemic attack.

The final question, “What is good diabetic control?” is more difficult to answer. It goes beyond ONLY blood sugar control, however good the HbA1c may be.

The aim of diabetic treatment is not merely to chase after a figure, be it the HbA1c or blood sugar level. It is to prevent the complications of diabetes, like damage to the eyes, kidneys, nerves, and also to prevent heart attacks and strokes.

Good control means that the patient will remain free of these complications and his or her life will be as normal as possible. A holistic approach is necessary – scrupulous attention to weight, blood pressure and cholesterol levels is also important.

Your doctor will be the best guide – DO NOT self-medicate.

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