How is the Diagnosis of Diabetes made?
One of the simplest tests which may show the presence of diabetes is a urine 'dipstick' test. This test detects glucose or sugar in the urine. When blood glucose levels are high glucose can spill over into the urine and can then be detected with a urine test. Urine testing for glucose is a useful screening test for diabetes.
Having glucose in the urine may indicate that you have diabetes but the diagnosis of diabetes is only really confirmed when a blood test shows high levels of blood glucose. Often the blood test needs to be done after you have fasted overnight. Sometimes if there is doubt about the diagnosis a second blood test is required or you may even be asked to have a special test known as a glucose tolerance test.
What is the normal blood glucose level and how high does the blood glucose need to be to mean I have diabetes?
Blood glucose levels can vary a bit throughout the day. Blood glucose levels rise up after a meal and then fall again sometime later. The blood glucose level falls overnight. Blood glucose levels measured before breakfast are very steady and in those without diabetes run between 3.5 to 6.0 mmol/l. Measuring the blood glucose level after an overnight fast and before eating breakfast is the most accurate test for diagnosing diabetes. This is known as a fasting blood glucose. A level of 7.0 mmol/l or higher means you have developed diabetes.
Sometimes the diagnosis of diabetes can be made on a blood sample taken at other times of the day and without you having to fast. If you have a lot of diabetes symptoms and a blood test shows your blood glucose to be over 11.0 mmol/l then a diagnosis of diabetes can confidently be made.
One other thing to remember, diabetes can only be diagnosed from a blood sample taken from your arm. Checking your glucose level by a finger prick blood test is not a reliable enough way of making the diagnosis.
Why do I need a Glucose Tolerance Test and what exactly is it?
If there is some doubt as to whether you have diabetes or not you may be asked to have a glucose tolerance test. Also sometimes if your fasting blood glucose results are on the borderline between normal and diabetes you may have an early form of diabetes which is known as ‘impaired glucose tolerance’. A glucose tolerance test is the way to check and see if this is the case. Glucose tolerance tests are also used in pregnancy to confirm whether a pregnant woman has developed gestational diabetes.
A glucose tolerance test measures how well your body deals with sugar (glucose). After an overnight fast, your blood glucose levels are measured just before and then two hours after you take a sugary drink. The drink is very sweet and contains 75g of glucose. If your blood glucose level two hours after taking the drink is over 11.0 mmol/l then this confirms you have diabetes.