Diabetes: get tested

What is a blood sugar test?

A blood sugar (glucose) test is a blood test that screens for diabetes by measuring the level of glucose in your blood. It is also used to monitor glucose levels in people with diabetes.

There are different types of blood glucose tests; for an initial screening test you may have a fasting blood glucose test, or a random, “casual”, blood glucose test. If you also have symptoms of diabetes, or risk factors, your doctor may order different or additional tests. Many pregnant women are also tested for gestational diabetes. Tests include:

  • Fasting blood glucose test: measures blood glucose after you have fasted (not eaten or drunk anything except water) for at least 8 hours. It’s convenient to get tested in the morning after you’ve slept (and naturally fasted) for around 8 hours. 
  • Random, or “casual”, blood glucose test:measures blood glucose regardless of when you last ate. This finger-prick test can be done at most pharmacies and clinics, and quickly indicates if there's a likelihood of diabetes. This test can also be used to take several measurements in the course of a day: glucose levels in a healthy person should not vary greatly.
  • 2-hour postprandial blood sugar test:measures blood glucose 2 hours after a meal. Blood glucose rises after eating, but 2 hours afterwards the level usually goes back down in healthy people.
  • Oral glucose tolerance test:a series of blood glucose measurements taken after a sweet glucose drink.

What the numbers mean

Your doctor will discuss your results with you and consider them in relation to your general health. Several conditions and factors can cause abnormally high blood glucose. 

In some people, blood glucose levels are abnormally low: this has different causes to high blood glucose. The medical term for low blood glucose is hypoglycaemia (”under” glucose); high blood glucose is termed hyperglycaemia (“over” glucose).

Who should be tested?

Everyone over age 45 should have their blood glucose tested; some medical experts recommend starting earlier, at age 40. Your results will indicate whether or how often you need to repeat the test.   

Talk to your doctor about your family history and risk factors for diabetes and heart disease – it may be advisable to start testing earlier. Diabetes South Africa recommends testing every year if you are over 35 and have any of the risk factors listed below.

Risk factors for type 2 diabetes

If any of these apply to you, you are at increased risk for diabetes:

  • Overweight or obese
  • Physically inactive
  • Family history: a parent or sibling has diabetes. Diabetes is more likely for some ethnicities. People of South Asian descent, for example, have higher risk; in South Africa, the Indian population has the highest incidence.
  • Women who developed diabetes during pregnancy
  • High blood pressure
  • High cholesterol          

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