Diabetes Diagnosis: How To Test For Diabetes

Diabetes Diagnosis: How To Test For Diabetes

Getting a prompt diabetes diagnosis can help you get the treatment you need, prevent complications and protect your future health. Certain signs and symptoms can indicate that you may have diabetes, but tests can confirm your diagnosis. 


How is diabetes diagnosed?


Your doctor will diagnose diabetes from your clinical history, an examination and blood tests. Common signs and symptoms of diabetes include: 

  • Passing urine more frequently
  • Increased thirst, despite drinking plenty of fluids
  • Feeling weak, tired and lacking in energy
  • Sudden weight loss
  • Feeling more hungry
  • Recurrent infections, including candida infections of the mouth or genitals
  • Cuts take longer to heal
  • Blurred vision
  • Fruity smelling breath

Children may complain of recurrent tummy pain, headaches or exhibit behavioural problems.


Getting tested for diabetes


If you are worried about diabetes or think a loved one may be affected, your doctor will need to do blood tests to measure the glucose in your blood.

Your GP can arrange blood tests and send the samples to the pathology laboratory for analysis if you are well in yourself. The results will usually come back in 1-3 days. 

If you are acutely unwell, you will need to be seen as an emergency. Call 111, seek an urgent appointment with your GP or attend your local accident and emergency department. If you are in hospital, the team can send the sample to the hospital laboratory, and you should have the results in under two hours. 


Can you test for diabetes at home?


Some home tests can indicate that you may have diabetes but won’t confirm the diagnosis. You should always see your doctor to send a blood sample to the lab and get a definitive diagnosis.

  • A simple finger prick test can show high blood sugar levels
  • A urine dipstick will show if your kidneys are leaking glucose


Blood tests for diabetes


Your doctor will usually check the concentration of glucose in your blood. They may do a finger pin prick test to get an immediate indication of your glucose levels. However, they should always do a blood test from a vein in your arm to confirm the results:


Random venous plasma glucose concentration


The nurse can take the sample at any time of the day. If you have a blood glucose of 11.1 mmol/l or more and diabetes symptoms, this indicates diabetes. If you don’t have any symptoms, your doctor will repeat the test, arrange a test when you have fasted, or organise an oral glucose tolerance test (OGTT).


Fasting plasma glucose concentration (FPG)


The nurse will take this after you have fasted for at least eight hours. You can’t eat or drink anything but water. It’s usually easiest to arrange this test first thing in the morning. If you have a fasting blood glucose of 7.0 mmol/l, this indicates diabetes. 


Oral glucose tolerance test (OGTT)


An OGTT is a test in which your blood glucose levels are measured before taking a sugary drink and then retested at fixed intervals up to two hours after the drink. Your doctor can use an OGTT to diagnose type 2 or gestational diabetes. The test will also show if you have impaired glucose tolerance or prediabetes.




The HbA1c is a blood test that shows your average blood glucose levels over the previous two to three months. It is the best blood test used in the diagnosis of diabetes. 

The test is quick and straightforward. The nurse can take it at any time; you don’t need to have fasted. If your HbA1c level is 48mmol/mol or above, this indicates diabetes. 

If your HbA1c is between 42 and 48mmol/mol, you have prediabetes and are at risk of developing type 2 diabetes

If you don’t have any symptoms, your doctor should repeat the test to confirm the result. 

HbA1c is not used to diagnose diabetes in children and young people, anyone suspected of having type 1 diabetes, patients who have had symptoms for less than two months, patients who are acutely ill, patients taking medication that can cause rapid glucose such as steroids, people with certain blood disorders and pregnant women.


Diagnosis of type 1 diabetes


When you first develop type 1 diabetes, it’s essential to get fast and effective treatment. You are at risk of developing a serious diabetes complication called diabetic ketoacidosis or DKA. IN DKA, acidic ketones build up in the bloodstream, making you extremely unwell and leading to coma or death.


Symptoms and signs of diabetic ketoacidosis 

  • Nausea, vomiting and abdominal pain
  • Floppy and lethargic
  • Unconsciousness and coma
  • Ketones on the breath – a fruity smell like pear drops
  • Dehydration
  • A deep, laboured pattern of breathing

Your doctor will diagnose type 1 diabetes if you present with symptoms of diabetes and your random plasma glucose is more than 11 mmol/L. They may dip your urine to check for glucose and perform a finger prick to get a rapid result. Type 1 diabetes is more likely in children and adults with:

  • Ketosis- fruity-smelling breath
  • Rapid weight loss
  • Younger than 50 years
  • BMI below 25 kg/m2
  • Personal or family history of autoimmune diseases

They will refer you or your loved one to a diabetes specialist team to confirm the diagnosis and provide treatment to control your glucose levels and balance your body’s fluids.


Diagnosis of type 2 diabetes


Many people with type 2 diabetes do not have any symptoms- their diabetes may be picked up on random screening or during treatment for something else. Talk to your GP if you are worried about diabetes symptoms, and don’t be afraid to ask for a test if they don’t offer you one. 

Your doctor will diagnose type 2 diabetes if you have:

  • Symptoms of diabetes such as thirst, passing lots of urine, blurred vision, unexplained weight loss, recurrent infections, and tiredness
  • Signs of diabetes such as darkening of the skin in the armpits, groin, and neck
  • Persistently high blood glucose on testing
    • HbA1c of 48 mmol/mol (6.5%) or more
    • FPG of 7.0 mmol/L or more
  • Random plasma glucose of 11.1 mmol/L 

One abnormal HbA1c or FPG level can diagnose diabetes if you have symptoms, although most doctors will repeat to confirm the result. If you don’t have symptoms, you should have repeat testing. Your doctor should then monitor your progress and test again as needed. 


To find out more about diabetes diagnosis, or to speak to one of our specialists at the London Diabetes Clinic about prospective treatment options, contact us today.






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Carol Willis

Carol Willis - Diabetes Clinic Facilitator

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