The only way you can find out if you or a loved one has diabetes is from blood tests that measure you blood glucose (sugar) levels. These can be arranged through your GP.
A diagnosis of diabetes is always confirmed by laboratory results. You’ll usually get the results of your blood test back in a few days. If you have symptoms that came on quickly and you’ve been taken into hospital, the results should come back in an hour or two.
A finger prick test using a home testing kit may show you have high blood sugar levels but won't confirm you have diabetes.
A normal blood test result will show you don't have diabetes. But the result will also show if you have diabetes or are at risk of developing type 2 diabetes.
Signs and symptoms of diabetes
Anyone can develop diabetes. That’s why it’s important to get tested if you notice any of the signs or symptoms. These aren’t always easy to spot. In fact, type 2 diabetes is often diagnosed through blood tests for other conditions or health issues instead.
Always talk to your doctor about any symptoms you’re worried about, even if you’ve been tested. If you’re not offered a test, you can ask for one .
If you feel very unwell or your symptoms have come on quickly seek an urgent appointment with your GP or call NHS 111.
Testing for type 1 and type 2 diabetes
If diabetes is confirmed by the results of a blood test the type of diabetes you have is usually determined by factors like weight , age at diagnosis, family history and how quickly any symptoms came on. The test results can also indicate if you are at risk of developing type 2 diabetes even if you don’t have it now.
If you’re being tested for type 1 diabetes then further blood tests can check your blood ketone levels. Following this you may be sent to hospital for further assessment.
A simple new test developed by researchers called C-peptide can help identify if someone has type 1 or type 2 diabetes.
Testing for your risk of type 1 diabetes
Scientists have developed a type 1 diabetes risk test that looks for markers of diabetes in your blood that can show up months or years before any symptoms appear. These markers tell us that the immune system has started to plan an attack against the pancreas. If you have them, it means you’re at a high risk of being diagnosed with type 1 diabetes in your lifetime.
This test is not the same as a finger-prick test, that a doctor might do to diagnose type 1 diabetes if you already have symptoms.
Type 1 diabetes screening isn’t yet available in the UK outside of research studies. We've got more information about who can get involved in these research studies.
Blood tests used to diagnose diabetes
We will explain below the different blood tests that could be used to diagnose your diabetes. Your doctor will ask you about any symptoms you have and will then decide which type of blood test to use.
Having blood tests doesn't need to be worrying, they’re straightforward and shouldn’t take very long. Depending on the test you have you may be required to fast beforehand. If you do need to fast, a healthcare professional will let you know in advance.
Non fasting blood tests - HbA1c
An HbA1c test is the main blood test used to diagnose diabetes. It tests your average blood sugar levels for the last two to three months. You don’t need to prepare for a HbA1c . It’s a quick and simple test where a small amount of blood is taken from a vein in your arm. This is different to a finger-prick test, which is a snapshot of your blood sugar levels at that moment.
You’ll normally get the test results in a few days. From these results, your healthcare professional will be able to see if you have diabetes. If you didn’t have any of the symptoms of diabetes before you were tested, you’ll need to have the test again to confirm the result.
You have diabetes if your HbA1c level is 48mmol/mol or above. You are at risk of developing type 2 diabetes (often known as prediabetes) if your HbA1c is between 42 and 48mmol/mol.
Random blood glucose test
If you have severe symptoms of diabetes, you may have a random blood test at any time of the day. This is a quick test, through a finger-prick or a vein in your arm.
If you have a finger-prick test, you’ll get the results straight away. If you have a blood test through a vein in your arm, you’ll get the results in a few days.
You or your loved one have diabetes if your blood glucose levels are 11.1mmol/l or more - regardless of how recently you ate.
But any diagnosis from a finger prick test will need to be confirmed by a blood test sent to a laboratory for results.
Fasting blood tests
Fasting blood sugar test
This is another blood test used to diagnose diabetes. It is sometimes called a fasting plasma glucose test or FPG for short. A nurse will take some blood from a vein in your arm. You’ll need to fast for at least eight hours before, without eating or drinking anything apart from water. This is to stop anything interfering with the results. Fasting overnight and taking the test in the morning is the easiest option if available. You’ll get the results in a few days.
You’ll be diagnosed with diabetes if your glucose levels are 7mmol/l or more.
Glucose tolerance test (GTT)
This blood test shows if your body is having problems handling the sugar you get from food and drinks. It is sometimes called an Oral Glucose Tolerance Test or OGTT for short. This test is used routinely when diagnosing gestational diabetes.
There are two parts. First, you have a fasting test. A nurse will take some of your blood from a vein in your arm and your blood glucose levels will be checked. You’ll then have a sweet drink, which contains a standard amount of sugar. This is to see if your body can maintain a normal blood sugar level. Two hours later, the nurse will take some mor of your blood and check your blood sugar levels again. You normally get the results in a few days. They’ll show different levels for the fasting test and the second test you did two hours later.
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