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byhyperglycaemia(elevated blood glucose level) leading to long-term complications.

Diabetes can be classified into a number of types:

• Insulin-dependent diabetes(Type 1) (also calledjuvenile diabetesandbrittle diabetes)is
  due to the autoimmune destruction ofb-cells in the pancreas. Generally it has a rapid
  onset with a strong genetic link.

Case study HYPOTHYROID CASE

A 59-year-old woman presented with a history of lethargy, cold intolerance and weight gain.

On examination, the doctor noticed that the patient’s hair appeared thin and her skin dry. Several tests

were requested including thyroid function tests the results of which were:

TSH¼ 46 : 9 mU dm^3 ðnormal range 0 : 4  4 : 5 mU dm^3 Þ

fT4¼ 5 : 6 pMðnormal range 9 : 0  25 pMÞ

These results indicate overt primary hypothyroidism. As the patient suffered from cardiovascular

disease the doctor commenced thyroxine replacement therapy at an initial dose of 25mg daily.

After 2 weeks, the tests were repeated:

TSH¼ 37 : 6 mU dm^3

fT4¼ 8 : 2 pM

These results remain abnormal so it was agreed that the tests should be repeated in 6 weeks’ time.

At this stage the results were:

TSH¼ 19 : 1 mU dm^3

fT4¼ 11 : 8 pM

These results confirm that either the thyroxine replacement dosage was inadequate or that compliance

was poor. As the patient confirmed that she had been taking the therapy as prescribed, the doctor

increased the dose to 50mg per day. After a further 8 weeks the tests were repeated:

TSH¼ 1 : 5 mU dm^3

fT4¼ 14 : 8 pM

The patient reported feeling much better and had improved clinically.

Comment The above results are typical of patients with hypothroidism, also referred to asmyxoedema. Primary
hypothyroidism due to thyroid gland dysfunction is by far the most common cause of the condition
but secondary (pituitary) and tertiary (hypothalamic) causes also exist. In these latter two cases the main
biochemical abnormality is a low fT4. TSH may be low or within the reference range in secondary
and tertiary hypothroidism, i.e. it does not respond to low fT4. Patients with primary hypothroidism
require lifelong therapy. Patients with cardiovascular disease, as in this case, must be initiated at a lower
dose than normal as over-treatment can lead to angina, cardiac arrhythmia and myocardial infarction.
Elderly patients are also started at a lower dose for the same reason. Once therapy has been commenced,
thyroid function tests should be carried out after 2–3 months to check for steady-state conditions
and thereafter repeated on an annual basis.

652 Principles of clinical biochemistry