Hyperuricaemia is defined as elevated levels of uric acid (≥7 mg/dL) in the blood and may be caused by either urate overproduction or underexcretion.

Clinical presentation

Patients with hyperuricaemia may be asymptomatic or have symptoms and signs relating to one of the complications of hyperuricaemia (e.g. gout, nephrolithiasis).

Pathology

Uric acid is produced as the end product of purine nucleotide degradation. Hypoxanthine and xanthine are the intermediates which are converted to uric acid via the enzyme xanthine oxidase. Uric acid is mostly excreted via the kidneys, the remainder being excreted intestinally, but up to 90% is resorbed via the transporters URAT1 and GLUT9 in the kidneys ^1,2. Hyperuricaemia may result from urate underexcretion, overproduction or a combination of both.

Aetiology

• underexcretion ³:

  • idiopathic

  • renal insufficiency

  • metabolic syndrome

  • drugs (e.g. diuretics)

  • pre-eclampsia and eclampsia

  • sarcoidosis

• overproduction:

  • idiopathic

  • Lesch-Nyhan syndrome

  • high purine diet

  • tumour lysis syndrome

  • haematological diseases (e.g. haemolytic anaemia, lymphoma, leukaemia)

• combined:

  • alcohol

  • glucose-6-phosphate dehydrogenase (G6PD) deficiency

Radiological features

No radiological features are specific for hyperuricaemia. Signs of complications of hyperuricaemia may be visible (e.g. gout, nephrolithiasis).

Treatment and prognosis 

Hyperuricaemia is treated by addressing the underlying cause of urate overproduction or underexcretion, xanthine oxidase and URAT1 inhibitors are also commonly used ². Hyperuricaemia is a risk factor for cardiovascular disease and gout ^2,3.