Type 1 diabetes mellitus

T1DM is characterised by complete, or near-complete, deficiency of insulin production from the pancreatic beta cells due to auto-immune destruction of pancreatic islets. Diagnosis is usually clinical but is supported by finding high titres of anti-islet cell, or anti-glutamic acid decarboxylase antibodies, and low levels of C-peptide in the face of hyperglycaemia. Treatment is mandatory insulin therapy.

FBC

Baseline haematological and biochemical investigations are mandatory in all newly presenting cases of diabetes.

Serum B12 and red cell folate

Pernicious anaemia may accompany T1DM as an auto-immune phenomena.

Urea and electrolytes

Patients with DKA may develop hyperkalaemia, dehydration and renal impairment. Assessment of urea and creatinine is also essential to gauge baseline renal function in any newly diagnosed case of diabetes.

Liver function tests

Baseline haematological and biochemical investigations are mandatory in all newly presenting cases of diabetes.

Bone profile

Baseline haematological and biochemical investigations are mandatory in all newly presenting cases of diabetes.

Fasting or random glucose

In most symptomatic cases the degree of hyperglycaemia will be such that there is no doubt about the diagnosis.

However, in borderline cases WHO criteria for diagnosis should be applied. These are that a fasting plasma glucose >7 mmol/L, or a random plasma glucose >11.1 mmol/L on one occasion in symptomatic patients or on two occasions in asymptomatic patients, indicates a diagnosis of diabetes mellitus.

If these criteria are not met it may be necessary to perform a 75 g oral glucose tolerance test. The same biochemical cut offs are used for the fasting and two hour values. 

All patients who are acutely unwell with diabetes must have a formal laboratory glucose assay, bed side glucometers are not sufficiently reliable in the acute, in-hospital setting.

9am or random cortisol

Many centres will not routinely assess cortisol at presentation but in any patient with diabetes who subsequently becomes unwell with frequent hypoglycaemia, unexplained weight loss and abdominal pains, lethargy or other vague constitutional symptoms, a random cortisol may be a useful test.

If it is greater than 550 nmol/L then no further action is needed. But, if not, it may be appropriate to proceed to a short synacthen test.

Thyroid stimulating hormone, free thyroxine

Hypothyroidism is routinely screened for at diagnosis as an auto-immune associate of T1DM.

Thyroid auto-antibody screen

Some centres routinely screen for thyroid auto-antibodies at diagnosis as an auto-immune associate of T1DM.

Coeliac auto-antibody screen

Coeliac disease is routinely screened for at diagnosis as an auto-immune associate of T1DM.

ECG

Not normally necessary but may be performed if there is suspicion of pre-exisitng ischaemic heart disease.

Fasting lipids

These are an important baseline but are often elevated before insulin therapy has been commenced.

HbA1c

This is often performed at diagnosis but in actual fact contributes very little at this stage as it will often be elevated. Conversely a normal HbA1c does not rule out the diagnosis as rapid onset hyperglycaemia may not yet be reflected in an elevated HbA1c.

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