Testing for diabetes

Posted on 12 November 2013

Diabetes Awareness Week is the perfect time to be screened and/or tested for this increasingly common condition. Here’s what you need to know about the different tests…

Diabetes is often referred to as ‘sugar’ because it’s associated with the prevalence of an excessive amount of glucose (a type of sugar) in the bloodstream. Insulin, the hormone produced by the pancreas, processes glucose in the blood, making it available as fuel for your body’s organs and cells. Insulin also helps your body store any excess glucose.

Diabetes mellitus is a chronic condition that occurs either when the body is unable to produce enough insulin (Type 1) or to use its insulin effectively to lower blood sugar (Type 2). This means that you land up with unusually high levels of glucose in your blood. High levels can be harmful, causing damage across the body, including kidney failure, heart attacks, blindness and strokes.

Since Type 2 diabetes, the more common one, can go undetected for years, it’s best to be screened for diabetes as part of your general health checkup. First, check the levels of glucose in your body. This can be done by having your urine or blood screened.

Urine screening
Your doctor may perform a simple dipstick test, to check the amount of sugar left in your urine after the renal threshold (‘spilling point’) has been reached.

The problem with urine screening is that it’s a ‘memory’ test; it shows sugar that could have been left over from hours before, and doesn’t give an accurate reading of the glucose in your system at that minute. For this reason, blood-glucose tests are more common. They can be taken using a simple skin-prick test at your local pharmacy or clinic, as well as in a doctor’s rooms.

The skin-prick blood-glucose test
This is a convenient way to check your likelihood of having diabetes, as it gives a snapshot of your glucose levels within one to five minutes.

A tiny needle takes a small blood sample, which is placed on a testing strip and analysed by a glucose-reading machine while you wait. It can either be done randomly (no fasted needed; best when there are diabetes symptoms present), or you may need to abstain from food or drink for eight hours before your appointment. If your results are high (blood sugar levels are over 200 milligrams per decilitre – mg/dL), you will need to have further tests.

Note: while skin-prick testing can show that there’s a high probability of diabetes, it’s not used for diagnosing the condition. For that, you’ll likely need to do a fasting blood glucose test.

The oral glucose tolerance test (OGTT)
Expecting mothers are usually tested for gestational diabetes (which can occur in up to 14% of pregnant women and normally disappears after birth) between 24 and 28 weeks, using the oral glucose tolerance test (OGTT). It’s also used to test for prediabetes and Type 2 diabetes.

You’ll have to fast from the night before the test. When you arrive, a blood sample will be taken in order to read your baseline glucose level. Then you’ll be given a sugary drink (75 to 100g), and your blood will be tested again, one to three times at regular intervals, and compared with your baseline. This will determine your tolerance to glucose (ie whether the insulin in your body is making proper use of the sugar ingested). This process can take up to four hours.

The haemoglobin A1C blood test
This is the primary laboratory test for diagnosing and managing diabetes. If you’ve shown a high reading on your skin-prick test, an A1C can confirm whether you have diabetes. It measures your average glucose level in your blood for a two- to three-month period by looking at haemoglobin, the oxygen-carrying proteins in red blood cells that typically live for three months. Glucose attaches itself to haemoglobin; this test determines the percentage of sugar attached to the haemoglobin in your blood.

Blood taken in a doctor’s rooms or pathologist lab is sent off to be analysed using a certified method. Below 5,7% is considered normal; while you may be diagnosed with diabetes if your haemoglobin A1C is 6,5% or higher (on two separate tests).

Note: Doctors usually test more than once for diabetes, often using both the skin-prick blood test and the HbA1C. This is because sometimes results for either will not be conclusive enough for a diagnosis. (For instance, anaemia, kidney disease, liver disease or low iron levels can interfere with the accuracy of a HbA1C result.)

If you’re diagnosed with either Type 1 or Type 2 diabetes, your doctor will check your HbA1C levels regularly as part of your treatment plan. Your doctor may also want to test for ketones, which form when the body burns fat or muscle, rather than glucose, for energy, using a urine or blood test. In addition, your C peptide levels (amino-acid proteins) will be checked, to test the ability of your pancreas to produce insulin, using the C-peptide test. These two further tests help in specifying whether you have Type 1 or Type 2 diabetes.

Who should be screened?
Ideally, everyone, but especially:
–    If you have increased thirst and urination; weight loss; blurred vision; fatigue; and extreme hunger.
–    A family history of diabetes or women who were diagnosed with gestational diabetes.
–    If you are overweight or have high cholesterol, high blood pressure or vascular conditions.

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The information provided in this article was correct at the time of publishing. At Mediclinic we endeavour to provide our patients and readers with accurate and reliable information, which is why we continually review and update our content. However, due to the dynamic nature of clinical information and medicine, some information may from time to time become outdated prior to revision.

Published in Diabetes

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