Screening and Diagnosis of Type 2 Diabetes


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This guideline is not suitable for people 25 years and under and does not apply to ongoing MONITORING of people with pre-existing diabetes.

Please note: HbA1c increases slightly with age alone. For patients 75 years and over, if the patient does not have clear signs/symptoms of diabetes, it is suggested to measure fasting glucose or do oral glucose tolerance test as the second confirmatory test for diabetes diagnosis.

In patients without symptoms but with an HbA1c ≥ 48 mmol/mol, repeat  HbA1c within 2 weeks (to confirm result and exclude any sampling/analytical error) and consider the factors listed below where HbA1c will not be reliable. If the second sample is <48 mmol/mol treat as high risk of diabetes and repeat the test in 3-6 months or sooner if symptoms develop. 

When NOT to use HbA1c to diagnose Type 2 diabetes

  1. Rapid onset of diabetes :
    1. Suspected type 1 diabetes –rapid onset of symptoms, weight loss, ketosis
    2. Children – because most will have type 1 diabetes
      Both conditions require same day specialist diabetes team contact
    3. Steroids , antipsychotic & immunosuppressant drugs
    4. After pancreatitis or pancreatic surgery
  2. Pregnancy : The diagnosis of gestational diabetes should be made by using glucose measurements in line with SIGN guidance

Fasting glucose - 5.1 mmol/L or above
2 hr glucose in GTT - 8.5 mmol/L or above

  1. Conditions with reduced red survival:
    1. Haemoglobinopathy eg sickle trait, sickle disease or thalassaemia
    2. Haemolytic anaemia
    3. Severe blood loss
    4. Splenomegaly
    5. Antiretroviral drugs
  2. Renal dialysis patients
  3. Iron and B12 deficiency and their treatment
  4. Individuals 25 years and under 

If use of HbA1c is not appropriate, diagnose diabetes based on fasting plasma glucose greater than or equal to 7.0mmol/l or random plasma glucose greater than or equal to 11.1mmol/l, repeating the test if individual is asymptomatic. If fasting plasma glucose less than 7mmol/l & clinical suspicion of diabetes then proceed to 75g Oral Glucose Tolerance Test


Abbreviation Meaning
HbA1c Haemoglobin A1c
T2D Type 2 diabetes
GTT Glucose tolerance test

Last reviewed: 12 May 2020

Next review: 31 May 2023

Version: 5.1

Approved By: TAM subgroup of ADTC

Reviewer Name(s): Consultant Physician

Document Id: TAM163