Differentials
Transient hyperglycaemia (e.g., from stress, corticosteroids, parenteral/enteral nutrition)
SIGNS / SYMPTOMS
In corticosteroid-induced hyperglycaemia, there is a clear history of corticosteroid use (including possible intramuscular injections of corticosteroids).
INVESTIGATIONS
HbA1c normal (reflecting normal blood glucose before the illness).
Type 1 diabetes mellitus
SIGNS / SYMPTOMS
Onset often at age <35 years, but it can occur in older individuals.[1] Many patients are not obese.[1] More commonly presents with symptoms (polyuria, polydipsia, weight loss, generalised weakness, blurred vision) and ketosis, rather than being detected by screening.[30]
INVESTIGATIONS
Low (<200 pmol/L [<0.6 ng/mL]) or absent C-peptide level.[1]
One or more autoantibodies (such as anti-glutamic acid decarboxylase 65 [GAD65] antibodies, islet cell antibodies [ICA], insulin autoantibodies, autoantibodies to the tyrosine phosphatase-related islet antigen-2 [IA-2 and IA-2beta], and zinc-transporter-8 [ZnT8] antibodies) are present in 85% of patients with type 1 diabetes at diagnosis, but may disappear within a few years.[1][31][32]
Glucose screening criteria cannot be used to differentiate type 1 and type 2 diabetes, as they are identical.[1]
Type 2 diabetes mellitus
SIGNS / SYMPTOMS
Older age (most patients >35 years; greater likelihood with increasing age) and slow onset of illness, obesity, a strong family history, absence of ketoacidosis, and initial response to oral antidiabetic drugs are typical of type 2 diabetes.
Clinical signs of insulin resistance (such as acanthosis nigricans) may be present.
Signs of more marked insulin deficiency (for example, glycaemic lability as well as susceptibility to ketosis) raise suspicion of type 1 diabetes.
INVESTIGATIONS
C-peptide present (>200 pmol/L [>0.6 ng/mL]).
Autoantibodies absent.
Testing for C-peptide and autoantibodies usually not required.
Glucose screening criteria cannot be used to differentiate type 1 and type 2 diabetes, as they are identical.[1]
Pre-diabetes
SIGNS / SYMPTOMS
Risk factors and history similar to those of type 2 diabetes.
INVESTIGATIONS
Impaired fasting glucose: 5.6 to 6.9 mmol/L (100-125 mg/dL).
Impaired glucose tolerance: plasma glucose is 7.8 to 11.0 mmol/L (140-199 mg/dL) 2 hours after 75 g oral glucose.
HbA1c of 39-47 mmol/mol (5.7% to 6.4%) indicates pre-diabetes or high risk of future diabetes.[1]
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