Does woman patient's raised uric acid require treatment?
What investigations should be
Initially, you would need to exclude an inflammatory arthropathy with an ESR or viscosity, rheumatoid factor, C reactive protein and, possibly, an autoimmune screen.
Assuming these are normal, we should investigate sinister causes for the raised uric acid. It should be clear from the records whether she is taking any medication such as diuretics, but also ask whether she is buying anything from the chemist such as regular aspirin.
A simple examination should include height, weight and blood pressure.
Renal function with urea and electrolytes and creatinine are important, although many laboratories will automatically perform these tests with the uric acid test. If there is any concern over her renal function a creatinine clearance can be carried out.
How common is an isolated raised uric acid in the UK population?
A raised uric acid is defined as a level above 420µmol/l in men and post-menopausal women and 360µmol/l in pre-menopausal women. It affects up to 8 per cent of the population. In otherwise healthy women it rises with age. There is also a slight diurnal variation.
The most important predictor of raised uric acid is body weight. It is unrelated to other factors such as social class, and there is no evidence that incidence is increasing.
Why do some patients have raised levels?
Patients with hyperuricaemia either under-secrete or over-produce urate. The commonest metabolic abnormality is a decrease in the urinary excretion of urate. The most likely reason for under-secretion is endogenous, which may be familial. Weight and hypertension are important independent factors. It is a particular problem in the elderly.
Under-secretion of urate may also be caused by poor renal function, although the uric acid level does not rise until the glomerular filtration rate falls below 20ml/min as measured by creatinine clearance. Some drugs reduce urate secretion, notably the thiazide and loop diuretics, low-dose aspirin and excess alcohol. Cyclosporin A used in transplant patients can also lead to hyperuricaemia.
Overproduction of uric acid may occur from excess purine consumption, excess red-cell breakdown in polycythaemia or haemolytic anaemia and acute tumour lysis in patients treated with radiotherapy and chemotherapy, especially for lymphoproliferative malignancy.
Systemic diseases such as psoriasis and medication such as nicotinic acid may increase uric acid. There are some rare errors of purine metabolism such as familial juvenile hyperuricaemic nephropathy and the X-linked hypoxanthine phosphoribosyltransferase deficiency.
What are the risks associated with asymptomatic hyperuricaemia?
The major risk is gout, although the exact relationship between hyperuricaemia and gout is unclear. Only one in 10 patients with a raised uric acid develops gout.
It is possible to suffer gout with normal uric acid levels. The risk of gout is not directly related to the level of uric acid so there is no level at which gout is inevitable, although it does become more likely with increasing levels.
Although 8 per cent of Scots have raised uric acid compared with
6.6 per cent of English, the incidence of gout is far lower.
Formation of kidney stones and chronic urate nephropathy depend on other factors. Patients rarely get clinically significant renal impairment from hyperuricaemia alone and so isolated hyperuricaemia should not normally be treated.
Acute gouty nephropathy usually occurs with myeloproliferative or lymphoproliferative disease, with the obstruction of collecting ducts and ureters by precipitating uric acid crystals.
If high uric acid follows cytotoxic drugs or radiotherapy, allopurinol should be used to prevent acute renal failure. It can also be used in patients who are dehydrated.
Will a diet help?
If she is overweight, dietary advice to lose weight is important. Traditionally, gout is supposed to affect the red-faced retired colonel who eats red meat and drinks red wine. There is an element of truth in this. A low purine diet can reduce blood urate by up to 15 per cent.
This diet consists of reducing liver, kidney, red meat, small muscular fish such as sardines, and vegetables such as pulses and whole grain cereal.
Beer, lager, port and some wines also contain purines. Alcohol will also raise blood lactate concentration.
Although body weight is an important factor in raised uric acid, a 'crash diet' to reduce weight produces ketosis which, in turn, will raise urate levels still further.
Mrs Tugo, a 50-year-old patient, presents
to you with generalised joint pain. All basic investigations are normal except she had a raised uric acid at 620µmol/l. What do you do?
Dr Peter Moore advises.
· Gout becomes more likely with increasing levels of uric acid
· Most important predictor of raised uric acid is body weight
· Under-secretion of urate is a particular problem in the elderly, though it may also be caused by poor renal function
· Overproduction of uric acid may occur from excess
purine consumption, excess red-cell breakdown and acute tumour lysis
· Low purine diet can reduce blood urate by up to 15 per cent