Process if a patient requires a Glucose Tolerance Test (GTT)

As you will know, the ways to test for diabetes use HbA1c or plasma glucose. 

HbA1c is generally used for the diagnosis of diabetes mellitus, but an alternative test is required where HbA1c is contraindicated, such as patients with haemoglobinopathies, in children and young people and people with a short duration of symptoms1,2. A fasting or random glucose may be used to diagnose diabetes mellitus, however there are some circumstances where the 2 hour GTT will be required. 

The GTT should only be requested in specific circumstance, such as those found to have impaired fasting glycaemia. If advice is required, please contact BHRUT consultant biochemists by email  

As patients will need two appointments, the first followed by a sugar load and the second sample two hours later, patients who need this test should telephone 020 8970 8383 stating that they need a GTT. Two appointments will then be booked for them at the King George Hospital site. 


  2. WHO (2011) Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus: abbreviated report of a WHO consultation. World Health Organization.