Blood glucose tests are also sometimes called blood sugar tests. They can be done after you have fasted or as a test called an oral glucose tolerance test. They are usually used to check for or monitor diabetes.
This test measures the amount of glucose in your blood. Glucose is a simple sugar that provides energy for the body.
People with diabetes often monitor their own blood glucose at home. This is done using a finger-prick test and a special machine, rather than a blood sample taken from a vein.
You might have blood taken for a blood sugar level. You might or might not be asked to fast beforehand.
There is also a test called an oral glucose tolerance test, abbreviated as OGTT or GTT. For this test you fast, then have a blood sample taken, then drink glucose, then have a number of samples taken over a few hours.
Why would I need this test?
You might need this test if you are at risk of developing diabetes, or if you have had any symptoms or test results suggesting diabetes.
The standard blood glucose tests measure your blood sugar level at a particular time. The OGTT measures how you respond to glucose.
Pregnant women can develop a particular type of diabetes called gestational diabetes, and will be asked to have an OGTT around 24 to 28 weeks of pregnancy. Gestational diabetes usually goes away after the baby is born.
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How to prepare for this test
If you’re asked to fast, you can’t eat anything for 8 to 10 hours before the test. You should drink only water.
If you are having an OGTT, you will need to adjust your diet for a few days before the test and fast for 8 hours just before the test.
Understanding your results
High levels of glucose can indicate diabetes or being at risk of diabetes. There are other conditions that can also cause high glucose levels. You will need to discuss with your doctor what the test results mean for you, given your specific circumstances.
More information
About blood glucose testing
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About blood testing
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- what to consider before having the test
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This test is done to evaluate how your body is processing sugar and to determine if you have developed Gestational Diabetes (Diabetes of Pregnancy).
The test requires a total of four blood draws. The first is done fasting (after you have had nothing to eat or drink for at least 8-12 hours prior—except water).
Then you will be given a glucose liquid to drink that has a specific amount of sugar in it. Blood samples will be taken one, two, and three hours after you have completed this drink.
In preparation for this test:
- You should eat your normal diet prior to the day of testing.
- Do not eat, drink, smoke, or exercise for at least 8-12 hours before your first blood sample is taken. You may drink plain water but no other beverages.
- This test may take up to four hours to complete. Activity can interfere with the results so you will need to remain in the lab for the duration of the test.
- Consider bringing something to read or a project to work on while waiting.
- You may drink water so feel free to bring your own cup or water bottle.
- Once the test is completed, you may resume normal eating and drinking. You may be hungry once the test is finished, so you may want to bring along a light snack to eat before leaving or driving home.
Gestational Diabetes is typically diagnosed when two or more of the results are elevated. Your doctor may also use other criteria to make the diagnosis.
Video Transcription:
Hi, I’m Nicole, I’m a nurse here at Moreland OB-GYN and I‘m here to you about our two glucose tests that we do during pregnancy. These tests measure the pregnant women’s reaction to glucose and screen for gestational diabetes which is a condition when a woman that does not have diabetes ends up with elevated high glucose levels. Having elevated blood sugar during pregnancy can affect your baby and your delivery. Advanced maternal age, your activity level, being overweight, or having a family member with diabetes all are factors that can contribute to gestational diabetes. First, I will explain the 1-hour glucose test, otherwise known as O’Sullivan Testing. You will be given a drink, like this, typically at your 24-week prenatal visit. You will be expected to drink the liquid prior to your next visit between 26 and 28 weeks of pregnancy. You need to drink this within 5 minutes, and then you will have to have your blood drawn one hour from that time. What does the drink taste like? It’s very sweet so we recommend drinking it straight from the fridge so it’s nice and cold to help control that sweetness. It is recommended to avoid foods or snacks that are high in sugar prior to the test. A normal or negative test result means you do not have gestational diabetes. However, an abnormal or positive test result means you are at risk for having gestational diabetes and we will need you to do the three-hour glucose test. So how does the three-hour test work? There are multiple blood draws for the three-hour glucose test, the first after fasting for 8-12 hours. Then you will be given a similar glucose liquid to drink and blood samples will be taken at 1, 2, and 3 hours after completing that drink. Because activity can interfere with the results, you will need to stay in the lab during the duration of the test, so we recommend bringing something to read, a project to work on, something to watch while you are waiting. You may drink plain water during the test however no food can be consumed at the time. Bring a snack for after cause you may be quite hungry. Based on the results of this test and other criteria that your doctor uses, you will be given a diagnosis. If you’re positive after this test, your physician will provide you information and other resources on how to manage your gestational diabetes. We hope this video gave you an overview of the testing performed to check for gestational diabetes. We have additional information on our website – Moreland o-b-g-n dot com, and if you still want more information, please ask your physician at your next visit. As always, it's our job here at Moreland to lead women to better health.
Dr Partha Kar
If your glucose level remains high then you have diabetes. If the level goes too low then it is called hypoglycaemia.
The main tests for measuring the amount of glucose in the blood are:
- Random blood glucose level.
- Fasting blood glucose level.
- The HbA1c blood test.
- Oral glucose tolerance test.
- Capillary blood glucose (home monitoring).
- Urine test for blood sugar (glucose).
Random blood glucose level
A sample of blood taken at any time can be a useful test if diabetes is suspected. A level of 11.1 mmol/L or more in the blood sample indicates that you have diabetes. A fasting blood glucose test may be done to confirm the diagnosis.
A glucose level below 11.1 mmol/L on a random blood sample does not rule out diabetes. A blood test taken in the morning before you eat anything is a more accurate test. Do not eat or drink anything except water for 8-10 hours before a fasting blood glucose test. A level of 7.0 mmol/L or more indicates that you have diabetes.
If you have no symptoms of diabetes but the blood test shows a glucose level of 7.0 mmol/L or more, the blood test must be repeated to confirm you have diabetes. If you do have symptoms and the blood test shows a glucose level of 7.0 mmol/L or more, the test does not need to be repeated. See the separate leaflets called Type 1 Diabetes and Type 2 Diabetes for more details.
This test is not now usually used to diagnose diabetes. However, the test may be done if it is thought your body doesn't control glucose levels normally but not badly enough to be called diabetes. This is referred to as pre-diabetes (impaired glucose tolerance). The test may also be used to see whether a woman has developed diabetes associated with pregnancy.
For this test, you fast overnight. In the morning you are given a drink which contains 75 g of glucose. A blood sample is taken two hours later. Normally, your body should be able to deal with the glucose and your blood level should not go too high. A glucose level of 11.1 mmol/L or more in the blood sample taken after two hours indicates that you have diabetes. See the separate leaflet called Glucose Tolerance Test for more details.
The HbA1c blood test
If you have diabetes, your HbA1c level may be done every 2-6 months by your doctor or nurse. This test measures your recent average blood sugar (glucose) level. Because it is an average measurement you do NOT need to fast on the day of the test. The test measures a part of the red blood cells. Glucose in the blood attaches to part of the red blood cells. This part can be measured and gives a good indication of your average blood glucose over the previous 2-3 months.
- In the UK HbA1c results used to be expressed in percentages in line with the Diabetes Control and Complications Trial (DCCT). The non-diabetic 'normal' range is 4-6%.
- Since 1st June 2009, HbA1c results in the UK have been standardised to the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). The equivalent normal non-diabetic range is 20-42 mmol/mol.
| Comparing DCCT-HbA1c and IFCC-HbA1c Results | |
| DCCT-HbA1c (%) | IFCC-HbA1c (mmol/mol) |
| 6.0 | 42 |
| 6.5 | 48 |
| 7.0 | 53 |
| 7.5 | 59 |
| 8.0 | 64 |
| 9.0 | 75 |
For people with diabetes, treatment aims to lower the HbA1c level to below a target level which is usually agreed between you and your doctor at regular check-ups. Ideally, the aim is to maintain your HbA1c to less than 48 mmol/mol (6.5%). However, this may not always be possible to achieve and the target level of HbA1c should be agreed on an individual basis between you and your doctor. (For example, by increasing the dose of medication, improving your diet, etc.)
It is now recommended that HbA1c can also be used as a test to diagnose diabetes. An HbA1c value of 48 mmol/mol (6.5%) or above is recommended as the blood level for diagnosing diabetes. People with an HbA1c level of 42-47 mmol/mol (6.0-6.5%) are at increased risk of diabetes and cardiovascular disease. See the separate leaflet called Pre-diabetes (Impaired Glucose Tolerance) for more details.
A drop of blood from a finger prick is placed on a test strip which contains a chemical that reacts with glucose. By using a colour chart or a small glucose meter machine, the blood level of glucose can be measured quickly. Home monitoring is very important for any person with diabetes who needs insulin treatment.
Urine (produced by the kidneys) does not normally contain glucose. The kidneys filter our blood, keeping substances the body needs, while getting rid of waste products. Your kidneys constantly reabsorb glucose so that it doesn't enter your urine. However, if the glucose level goes above a certain level, the kidneys can't reabsorb all of the glucose. This means that some glucose will 'spill' through the kidneys into the urine.
A simple dipstick test can detect glucose in a sample of urine. In a dipstick test a doctor or nurse uses a special chemical strip which he/she dips into a sample of your urine. Colour changes on the strip show whether there is glucose in the urine sample. If you have glucose in your urine, you are likely to have diabetes.
However, some people have kidneys that are more 'leaky' and glucose may leak into urine with a normal blood level. Therefore, if your urine contains any glucose, you should have a blood test to measure the blood level of glucose to confirm, or rule out, diabetes.