Diabetes is broadly classified into Type 1 Diabetes Mellitus (T1DM) and Type 2 Diabetes Mellitus (T2DM).
T2DM is a chronic heterogeneous polygenic disorder influenced by multiple risk factors.
The natural history of diabetes involves three stages which usually take years before the diagnosis.
People with diabetes pass from normal glucose tolerance (1) to pre-diabetes (2) further ending up with frank diabetes (3).
Several risk factors dictate the rapidity of T2DM onset.
Normal glucose tolerance is defined by
- Fasting plasma glucose < 100 mg/dl
- 2 hours (post 75 gms oral glucose tolerance test) < 140 mg/dl
- HbA1c ≤ 5.6%
Pre-diabetes is an intermediate stage which is defined by:
- Fasting plasma glucose : 100 – 125 mg/dl
- 2 hours (post 75gms oral glucose tolerance test) : 140 – 199 mg/dl
- HbA1c : 5.7 – 6.4%
This phase is vital for at least three reasons:
First being its estimated prevalence in India is alarming 14%, and the majority of them are asymptomatic.
Secondly, the risk of progression from this stage to diabetes is 5-50% within 5 years, and clinical trials have shown that a balanced diet coupled with exercise and weight loss can dramatically mitigate this risk.
Some of the complications like diabetic neuropathy and other comorbidities like hypertension, obesity and dyslipidemia (abnormal blood lipids) are found to be prevalent in pre-diabetes which exacerbate the future risk of cardiovascular disease forming the last reason.
Frank diabetes is defined by :
- Fasting plasma glucose ≥ 126 mg/dl
- 2 hours (post 75 gms oral glucose tolerance test) ≥ 200 mg/dl
- HbA1c ≥ 6.5%
T1 DM is due to autoimmune (i.e. own immunity acting against our organs) destruction of insulin-secreting beta cells in genetically predisposed individuals.
It is characterised by childhood onset with extremely high blood glucose levels.
American diabetes association (ADA) classifies T1 DM pathophysiologically into three stages:
- Auto-antibodies positivity with normal glucose levels in asymptomatic subjects being the first stage.
- Deranged blood glucose levels along with auto-antibodies denote second.
- And these seen collectively in a symptomatic patient constitutes the final stage.
These are similar to T2 DM stages but progress rapidly and generally difficult to discern these stages in patients, so clinical trials of T1 DM prevention focus on the first degree relatives of T1DM patients.