Examination
17615
Urate (Uric Acid)
Purpose of test
The main reason for requesting a urate include:
1. serum urate is usually measured 4 – 6 weeks after an
acute attack of gout to confirm hyperuricaemia.
Hyperuricaemia predisposes to gout but occasionally gout
can present in absence of raised urate
2. measurements of urate is essential to the monitoring of
urate lowering treatment
3. investigation of recurrent kidney stones
4. high urate can be a feature of pre-eclampsia (though is
not one of the diagnostic criteria)
5. monitoring/detecting tumour lysis syndrome in patient
undergoing chemotherapy
6. monitoring certain drugs treatments (e.g ethambutol,
pyrizinamide) which can reduce renal urate excretion and
cause hyperuricaemia: 50% of patients treated with
ethambutol develop hyperuricaemia
Sample
Blood
Sample Tube/Container
Adult- Yellow top or Green top Lithium Heparin Gel
Paediatric- Green top Lithium Heparin Gel
Sample Volume
4 ml
Minimum (see calculation of minimum volume)
Special Precautions
NICE CKS recommend sampling 4 – 6 weeks after an
acute attack of gout
Rasburicase can degrade uric acid in blood samples at
room temperature, leading to lower uric acid results than
are actually present, so special handling of samples is
necessary. Blood needs to be collected in pre-chilled
tubes containing heparin, either in the heparin sodium or
heparin lithium forms. After collection, the sample must
immediately be placed in an ice water bath and tested
within 4 hours of collection. These laboratory testing
procedures for uric acid must be followed for 4 days after
the last dose of rasburicase is administered
Request Form:
Clinical Chemistry & Haematology Requests
Laboratory
Biochemistry
Biological reference range
Female: 140 - 360 μmol/L
Male: 200 - 430 μmol/L
Clinical decision values
Incidence of gout is 1% at < 460μmol/L and 50% at
>540μmol/L
Factors affecting performance In sample where icterus (bilirubin), haemolysis or lipemia
is indicated by the manufacturer to cause inaccuracy of
>10%, the result will be dashed out or reported with a
disclaimer
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Calcium dobesilate causes artificially low uric acid results
Uricase reacts specifically with uric acid in-vitro causing
low results
In very rare cases, gammopathy, in particular type IgM
(Waldenström’s macroglobulinemia), may cause unreliable
results
Recovery may be falsely low when a blood sample is
taken while levels of N-Acetylcysteine(NAC), the
paracetamol metabolite N-acetyl-p-benzoquinone imine
(NAPQI), and Metamizole are still present
Venepuncture should be performed prior to the
administration of Metamizole
Venepuncture immediately after or during the
administration of Metamizole may lead to falsely low results
Turnaround times:
The Laboratory aims to report 90% of requests within the
stated time from receipt
Urgent - 1 hour
Ward - 4 hours
GP and OPD – 1 working day
Patient preparation
No specific requirements
Instructions for patient
collected sample
Lab Tests Online-UK is a useful source of information to
help patients understand the many clinical laboratory tests
that are used in diagnosis, monitoring and treatment of
disease. http://labtestsonline.org.uk/
Sample transportation
No specific requirements
Special handling needs
No specific requirements
Patient consent required
Implied consent
Specific rejection criteria
Generic rejection applies
Additional information
Additional test information is published by the Association
for Clinical Biochemistry and laboratory medicine in
Analyte Monographs alongside the National Laboratory
Medicine Catalogue (AMALC): Uric Acid
http://www.acb.org.uk/
Minimum Retest IntervalsMeasurement of urate in pre-eclampsia whilst not
admitted: twice weekly
Causes of high values
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1. Primary
• the majority of patients with primary gout have reduced
urate excretion rather than increased production, probably
due to increased tubular reabsorption
• there are several rare inherited metabolic diseases in
which hyperuricaemia occurs e.g. Lesch‐Nyhan syndrome
(caused by deficiency of hypoxanthine-guanine
phosphoribosyltransferase)
2. Secondary
• acidosis
• alcohol
• drugs
○ increasing tissue turnover e.g. cytotoxics
○ decreasing urate excretion e.g. thiazide diuretics
○ ciclosporin, low dose (<2 g/day)
○ salicylates
• high purine intake (offal, sardines and anchovies)
• increased tissue turnover (e.g. tumour lysis syndrome, in
which precipitation of urate crystals in the lumen of renal
tubules can cause obstructive nephropathy)
• starvation
• strenuous exercise
• lead poisoning
• obesity
• renal impairment
As Hyperuriceamia is associated with metabolic syndrome
so follow-up measurement of a lipid profile recommended
Causes of low values
Hypouricaemia is uncommon and of no clinical
consequence
References
- Lab Tests Online
- Roche insert 2011-01, V 4 English
- WHO use of anticoagulants in diagnostic laboratory
investigations
- National Minimum Re‐testing Interval Project: A final
report detailing consensus recommendations for minimum
re‐testing intervals for use in Clinical Biochemistry 2012
- NICE CKS Gout 2012
http://cks.nice.org.uk/gout#!diagnosissub:3
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