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Tests for Glucose (Sugar) and HbA1c

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If your blood glucose (sugar) level remains high then you have diabetes. If the level goes too low then you have hypoglycaemia.

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 blood 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.

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.

Fasting blood glucose level

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 (see the separate leaflet called Type 2 Diabetes) but the blood test shows a glucose level of 7.0 mmol/L or more then 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 then the test does not need to be repeated.

Oral glucose tolerance test

See also the separate leaflet called Glucose Tolerance Test.

This test may be done if the diagnosis of diabetes is in doubt. 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.

Home monitoring

A drop of blood from a finger prick is placed on a test strip which has a chemical impregnated which reacts with glucose. By using a colour chart or a small glucose meter machine, the blood level of glucose can be measured quickly.

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 glucose level. 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.

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. Ideally, the aim is to maintain your HbA1c to less than 48 mmol/mol (6.5%) but 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.

Original Author:
Dr Rachel Hoad-Robson
Current Version:
Peer Reviewer:
Dr John Cox
Document ID:
4786 (v39)
Last Checked:
Next Review:
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