One or more of the following blood tests will be done to diagnose if you have diabetes:
Fasting blood glucose test
After an overnight fast (nothing to eat or drink) of eight hours, blood is taken from a vein in your arm, by a trained nurse in a laboratory, for a glucose level. The results will be made available to your doctor to discuss.
Glucose tolerance test
This is also known as the oral glucose tolerance test (OGTT); it measures your body’s response to glucose. It can be used to screen for Type 2 diabetes and gestational diabetes.
This test must be booked in advance with the laboratory. Again, after an overnight (eight hours) fast, a sample of blood will be drawn from a vein in your arm to measure your fasting blood glucose level.
You will then be given a glucose solution to drink and two hours later your blood glucose will be measured again. If you’re testing for gestational diabetes, you will test after an hour, two hours and three hours and your doctor will consider the results of each blood glucose test
The OGTT can differentiate between pre-diabetes and diabetes according to the blood glucose levels (see table below).
Prediabetes due to a raised fasting blood glucose is called impaired fasting glucose. Prediabetes due to a raised two-hour blood glucose is called impaired glucose tolerance. It’s possible to have either or both.
DEFINITIONS OF PREDIABETES AND DIABETES AFTER A TWO-HOUR ORAL GLUCOSE TOLERANCE TEST*
| Fasting blood glucose mmol/L | Two-hour blood glucose mmol/L | |
| NORMAL | < 6,1 | < 7,8 |
| PREDIABETES | 6,1 – 6,9 | 7,8 – 11,0 |
| DIABETES | ≥ 7,0 | ≥ 11,1 |
*After an overnight fast, blood is taken for the fasting glucose sample; then the person is given a 75g glucose drink; a second sample is taken two hours later.
HbA1c
The haemoglobin A1c (HbA1c) test gives a percent average level of blood glucose over the past three months. No preparation is needed before the test. A sample of blood will be drawn from your arm and will be sent off to a laboratory where the results may take two to three days. In many doctors’ rooms this can be done on a point-of-care machine with a finger prick sample. An HbA1c ≥ 6,5% is accepted as a diagnosis of diabetes.
People with diabetes need a HbA1c test done regularly. Staying within an ideal range has been proven to prevent complications. This result, along with self-blood glucose measurements, will guide the need to adjust medication. The targets for HbA1c, fasting blood glucose and two-hour post meal glucose vary according to age.
TARGETS FOR GLUCOSE CONTROL
| HbA1c | Fasting blood glucose mmol/L | Two-hour post meal blood glucose mmol/L | |
| YOUNG | < 6,5% | 4 – 7 | 4,4 – 7,8 |
| MOST | < 7,0% | 4 – 7 | 5 – 10 |
| ELDERLY | < 7,5% | 4 – 7 | < 12 |
Urine test
Even though this isn’t used to diagnose diabetes, a urine test will show excess glucose in the urine. It’s also used to look for ketones (substances that are produced when there is a shortage of insulin). Ketones can lead to a serious condition called ketoacidosis so must always be reported to your doctor or DE.
Self-blood glucose test
Your finger is pricked to draw a small drop of blood. This blood is then wiped onto a test strip that will give a glucose reading within seconds. There are many reliable glucometer machines on the market.
Continuous blood glucose monitoring
There are several devices available that can be inserted into the skin of the abdomen or arm which read glucose levels 24/7; most will send these readings to a smartphone.
Header image by Adobe Stock