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The main diagnostic test for diabetes is taking a blood test to measure glucose, either when you have been fasting or at other times of the day. Diagnostic tests are also used routinely during pregnancy to identify gestational diabetes.
High blood sugar levels harm the body
The hormone insulin helps to move blood sugars (glucose) into cells and convert glucose into energy. Diabetes is a condition characterised by abnormally high levels of glucose in the blood. This occurs because either not enough insulin is made or the cells don’t respond to the hormone.
Untreated, high glucose levels can cause serious damage to many parts of the body, including:
- Kidney damage
- Eye damage
- Nerve damage to the feet and other parts of the body
- Heart disease and circulation problems in the legs
- Stroke
- Impotence.
Accuracy of test results
Depending on the test used, the level of blood glucose can be affected by many factors including:
- Eating or drinking
- Taking medications that are known to raise blood sugar levels, such as oral contraceptives, some diuretics (water pills) and corticosteroids
- A recent injury, physical illness or surgery that may temporarily alter blood sugar levels.
Test procedures
Most diabetes tests require blood samples. Generally, a band is tightened around your upper arm to slow blood flow and cause the veins below the band to stand out. The intended injection site is swabbed with alcohol. The hypodermic needle is inserted into the vein and the blood is directed into a collection tube. The band may be removed from your arm while the blood is being taken.
You may need more than one collection tube, depending on the test. After the blood is taken, you are asked to press a cotton ball or gauze against the injection site. Once bleeding has stopped, the injection site is covered with a sticking plaster.
Types of tests
Tests to diagnose diabetes include:
- Fasting blood glucose test – blood glucose levels are checked after fasting for between 12 and 14 hours. You can drink water during this time, but should strictly avoid any other beverage. Patients with diabetes may be asked to delay their diabetes medication or insulin dose until the test is completed.
- Random blood glucose test – blood glucose levels are checked at various times during the day, and it doesn’t matter when you last ate. Blood glucose levels tend to stay constant in a person who doesn’t have diabetes.
- Oral glucose tolerance test – a high-glucose drink is given. Blood samples are checked at regular intervals for two hours.
The most common test for diagnosis of diabetes is the fasting blood glucose test. Glucose tolerance tests are used when the results of the fasting blood glucose are borderline. They are also used to diagnose diabetes in pregnancy (gestational diabetes).
Immediately after the procedure
The fasting blood glucose test will confirm that the person has diabetes if it shows that the level of glucose in their blood is higher than normal when they are fasting.
Sometimes the test result of the fasting blood glucose test is borderline. If this is the case, a glucose tolerance test may be performed. This test will confirm diabetes if the person’s blood sugar levels stay high for a long time after the tests.
If a person doesn’t have diabetes, the results of the glucose tolerance test will show that their blood sugar levels fall within the normal range.
Possible complications
Possible complications of diabetes testing include:
- Some people feel faint or nauseous at the sight of blood or needles
- Bleeding and bruising at the injection site
- Infection of the skin at the injection site
- Multiple injection sites if collecting the blood is difficult
- A reaction following the oral glucose tolerance test if the patient has diabetes mellitus or hypoglycaemia (low blood sugar levels) – medications may be needed.
Taking care of yourself at home
Be guided by your doctor, but generally there are no special instructions to follow after having a diabetes test.
Long-term outlook
Gestational diabetes is a temporary condition that usually resolves by itself once the baby is born. Regular monitoring throughout the pregnancy is recommended.
There is no cure for diabetes mellitus, but the condition can be managed. Treatment depends on the type of diabetes (type 1 or type 2), but the general aim is to control blood sugar levels and keep them within the normal range. Treatment options may include:
- Low fat, high carbohydrate diet
- Regular exercise
- Insulin injections or tablets
- Other medications as required.
Other blood glucose tests
A person with diabetes may regularly check their blood sugar levels at home using glucose test strips. This is a monitoring test, not a diagnostic test.
Where to get help
Things to remember
- There are various tests your doctor may wish to perform if you have symptoms of diabetes, including a random blood sugar test, a fasting blood sugar test or an oral glucose tolerance test.
- Factors that can affect the accuracy of test results include failure to follow pre-test instructions, recent injury or illness, and certain medications including oral contraceptives, corticosteroids and antidepressants.
- Be guided by your doctor, but generally there are no special instructions to follow after having a diabetes test.
You might also be interested in:
Diabetes.
Diabetes - gestational.
Diabetes and healthy eating.
Diabetes type 1 - juvenile diabetes.
Diabetes type 2.
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