Diabetes Distilled: WHO classification recognises changes in the diabetes landscape

By Colin Kenny, Editor – Diabetes Distilled

The World Health Organization (WHO) has updated its 1999 classification of diabetes. The new guidance distinguishes between type 1 and type 2 diabetes, as well as recommending conventional diagnostic methods. It also recognises hybrid forms of diabetes; with latent autoimmune diabetes in adults (LADA) becoming slowly evolving immune-mediated diabetes of adults; and ketosis-prone type 2 diabetes being recognised as a separate entity. Monogenic diabetes is now classified based on the mutated gene and the clinical syndrome. The guidance also draws attention to hyperglycaemia first detected during pregnancy and suggests clinicians should distinguish between type 1 or 2 diabetes first diagnosed during pregnancy and gestational diabetes.

The WHO expert panel has recognised that the phenotypes of type 1 and type 2 diabetes are becoming less distinct. With an increasing prevalence of obesity at a young age, they recognised the relatively high proportion of incident cases of type 1 diabetes in adulthood and the occurrence of type 2 diabetes in young people. The guidance acknowledges that there are hybrid forms of diabetes, including slowly evolving immune-mediated diabetes, which was formerly called LADA, and ketosis-prone type 2 diabetes. They also highlighted that developments in molecular genetics are allowing clinicians to identify a growing number of subtypes of diabetes. Clinical manifestations of monogenic defects in β-cell function include maturity-onset diabetes of the young, permanent neonatal diabetes, transient neonatal diabetes and genetic syndromes where insulin-deficient diabetes is associated with specific clinical features. 
 
The guidance recommends the four current diagnostic tests for diabetes. These tests involve the measurement of: 

• Fasting plasma glucose
• 2-hour post-load plasma glucose after a 75 g oral glucose tolerance test 
• HbA_1c
• Random blood glucose in the presence of signs and symptoms of diabetes.

 
In 2013, WHO updated its 1999 definition and diagnostic criteria for hyperglycaemia first detected in pregnancy. The new classification includes two categories of hyperglycaemia when first recognised in pregnancy: one is diabetes mellitus, defined by the same criteria as in non-pregnant persons; the other is gestational diabetes, defined by newly-recommended glucose cut-off points that are lower than those for diabetes. 

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