• Type 1, 2, or 3 Diabetes mellitus: 6.5% or 48 mmol/mol
• Gestational diabetes mellitus: 5.8% or 40 mmol/Lb*

*An Hba1c can be used to diagnose GDM if the OGTT is not being performed. It is less sensitive and specific than the OGTT, so is not recommended as a routine diagnostic test in GDM.

*A single blood test is a good clue to diabetes but is not sufficient to diagnose it. Perform the formal diagnostic test to confirm: an HbA1c for non-pregnant people and a 75g OGTT for GDM. 

• Type 1, 2 or 3 Diabetes mellitus: =7.0mmol/L
• Gestational diabetes mellitus: 5.1 – 6.9 mmol/L

*A single blood test is a good clue to diabetes but is not sufficient to diagnose it. Perform the formal diagnostic test to confirm: an HbA1c for non-pregnant people and a 75g OGTT for GDM. 

• Type 1, 2 or 3 Diabetes mellitus: =11.1mmol/L
• Gestational diabetes mellitus: 8.5 – 11.0mmol/L

• Type 1, 2 or 3 Diabetes mellitus: 
  • Fasting: =7.0mmol/L
  • 1-hour glucose: -
  • 2-hour glucose: =11.1mmol/L
• Gestational diabetes mellitus: 
  • Fasting: =5.1 mmol/L
  • 1-hour glucose: =10.0mmol/L
  • 2-hour glucose: =8.5 mmol/L

Clinical clues:

• Rapid, recent weight loss
• Slim body habitus
• DKA at presentation
• Younger age at diagnosis (although not always!)

Fasting c-peptide: Normal or low

Anti-islet cell antibodies: Positive in >85% cases

Clinical clues:

• Family history of T2DM
• Central obesity
• High risk ethnic background
• History of PCOS, NAFLD

Fasting c-peptide: High

Anti-islet cell antibodies: Negative

Clinical clues:

• History of pancreatitis or pancreatectomy
• Cystic fibrosis

Fasting c-peptide: Low

Anti-islet cell antibodies: Negative