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Familial dysalbuminaemic hyperthyroxinaemia, a thyroid trap
  1. P R Desai1,
  2. A P Lipscomb1,
  3. J Slater2
  1. 1St John’s Hospital, Chelmsford, UK
  2. 2Broomfield Hospital, UK
  1. Correspondence to:
    Dr P R Desai
    St John’s Hospital, Chelmsford CM2 9BG, UK;

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Paediatricians are frequently asked to see children who cause concern because of their slow growth or development. In this situation, despite the absence of any specific abnormal signs, thyroid function tests are commonly requested. They are nearly always normal.

We describe three patients, where abnormal results led to erroneous treatment for thyrotoxicosis. These patients had a diagnosis of familial dysalbuminaemic hyperthyroxinaemia (FDH), an interesting condition with euthyroid hyperthyroxinaemia where the patient is clinically euthyroid but has raised laboratory value of free thyroxine.1 Euthyroid hyperthyroxinaemia encompasses a broad range of conditions that can easily be misinterpreted as hyperthyroidism.2


A 7 year old girl referred to the hospital, was seen by general practitioner because of poor and abnormal thyroid function test results performed in primary care: total thyroxine 248 nmol/l (normal 80–150 nmol/l), free thyroxine 38 pmol/l (normal 10–25 pmol/l), and TSH 0.94 mU/l (normal 0.4–4 mU/l) (Bayer competitive assay for total and free thyroxine) (table 1).

View this table:
Table 1

 Initial investigations and treatment

Her pulse rate was 106 per minute but she had no other clinical features of thyrotoxicosis. Treatment was commenced with carbimazole (30 mg) after discussion with the paediatric endocrinologist.

Eighteen months later, while on treatment, the thyroid function tests remained abnormal (total thyroxine 105 nmol/l, free thyroxine 28.6 pmol/l, TSH 31.1 mU/l). This prompted the paediatrician to start block and replace therapy with additional thyroxine.

Two years from diagnosis, despite euthyroid clinical status and normal growth, biochemical control was still …

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