Testing for glucose

By DR MILTON LUM

DIABETES is a common condition. It is estimated that about 10% of the population are currently diabetics.

If left untreated or inadequately treated, diabetes is associated with complications that affect the heart, blood vessels, kidneys, feet, skin, genitals, eyes and brain. The health impact of these complications is considerable, eg 47% of new cases of end-stage renal failure are due to diabetes. The key to the prevention of the complications of diabetes is good control; one can then expect to live a normal life span free of complications.

Urine glucose

The urine is often tested for glucose. When the blood glucose is above a certain level, it spills into the urine. This can be easily tested by dipping a testing strip into the urine. The change in colour of the strip indicates there is glucose; the intensity of the change indicates the amount of glucose present. As most individuals do not normally have glucose in the urine, its presence would indicate the possibility of diabetes.

However, there may be spillage of glucose into the urine in some individuals whose blood glucose level is within the normal range – particularly during pregnancy. These people are said to have a lowered renal threshold. This places a limitation on urine glucose testing. So, when there is glucose in the urine, the doctor would advise testing for blood glucose to confirm or exclude diabetes.

Blood glucose

There are a few tests for blood glucose. After taking the blood from an individual, it is put into a bottle that contains substances which prevent the blood from clotting.

(a) Random blood glucose

This blood test is carried out at any time of the day when there is suspicion of diabetes. A reading of greater than 11 mmol/L indicates that the individual has diabetes.

(b) Fasting blood glucose

A random blood glucose level that is less than 11 mmol/L does not necessarily mean that the individual is not diabetic as the test is not 100% accurate. A measurement of the blood glucose after fasting overnight is much more accurate. If the blood glucose is greater than 6 mmol/L, it indicates that the individual has diabetes.

(c) Glucose tolerance test

This test is carried out when there is doubt as to whether an individual has diabetes. After he has fasted overnight, a drink containing 75g dose of glucose is given and a sample of blood is taken two hours later to test for blood glucose. A non-diabetic will be able to deal with this amount of glucose easily. If the blood glucose is greater than 11 mmol/L, then it indicates the individual has diabetes.

Additional tests

When a diagnosis of diabetes is made, the doctor will prescribe diet, exercise and, if necessary, medication to control it.

(a) HbA1c

Blood measurements of HbA1c are carried out periodically to assess the quality of blood glucose control. Blood glucose is attached to part of the red blood cells. A measurement of HbA1c provides information about the average blood glucose control in the preceding two to three months. The target should be a HbA1c of 7% or less. If the level is more than 7%, the doctor will advise additional measures to improve the diabetic control, eg more exercise and dieting, and additional dose of medication.

(b) Glucometer

Many diabetics use a home device called a glucometer to help them check on their control of the blood glucose. Their fingers are pricked and the blood obtained is applied to a strip that contains a chemical. The strip is then put into the glucometer to measure the blood glucose level in a short time. The doctor will advise on the frequency of testing and what to do when the results are available.

Blood lipids

Blood lipids cholesterol is a fat (lipid) that is produced by the liver from the fat in the food that we eat.

All of us have a certain amount of cholesterol in our blood for the body to carry out its various functions. The cholesterol is transported in the blood as part of compounds called lipoproteins. The high-density lipoproteins (HDL) prevent the formation of fat deposits in the arteries (atheroma) which is the main cause of cardiovascular disease like heart attacks and strokes. The low-density lipoproteins (LDL) are mainly involved in the formation of atheroma. The former is commonly called the “good” cholesterol and the latter the “bad” cholesterol.

Studies have reported that a 1% reduction of LDL will result in a 1% reduction in the risk of coronary heart disease.

The blood lipids reflect the amount of dietary fat in most people. This is not always the case as the same amount of fat intake can result in different levels of blood lipids in different individuals. However, in general, the lower the amount of fat consumed, the lower will be the blood lipids. Some individuals have high blood lipid levels because of certain conditions affecting them, eg obesity, excessive alcohol consumption, underactive thyroid gland.

Some families have high blood lipids because of an inherited genetic problem that affects the production of cholesterol. The measurement of blood lipids is also affected by acute stress or illness, e.g. fever, surgery, acute heart attack, and medicines, e.g. steroids, beta blockers, thiazides.

The blood lipids are measured, after an overnight fast, in a laboratory or by desktop machines which are found in many clinics. The results from desktop machines provide satisfactory results. It is common for more than one measurement to be taken because of biological and laboratory variability. The former is due to the fact that blood lipids are subject to variation for several reasons. The second sample is usually taken a few weeks after the first. The following values are considered desirable by doctors:
(a) Total cholesterol (TC) of 5.0 mmol/L or less;
(b) High-density lipoprotein (HDL) cholesterol of 1.2 mmol/L or more;
(c) Low-density lipoprotein (LDL) cholesterol of at least 3.0 mmol/L or less (the lower, the better);
(d) Triglycerides of 2.3 mmol/L or less; and
(e) TC/HDL, i.e. total cholesterol divided by HDL cholesterol ratio of 4.5 or less.
In general, the higher the cholesterol is, the greater the danger it poses to an individual’s cardiovascular health. In deciding on the risk, the blood lipids are among the factors considered. Other factors include age, sex, blood pressure, smoking, etc. Your doctor will advise you on the risk and what to do, if necessary, to achieve optimal cardiovascular health.


Excerpt from The Star
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Dr Milton Lum is Chairperson of the Commonwealth Medical Trust. This article provides general information only and is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation that the writer is associated with.