Uric acid - 24 hours urine

The Uric Acid - 24 Hours Urine test measures the total amount of uric acid eliminated through urine during a complete 24-hour period. Uric acid is a waste substance produced when the body breaks down purines. Purines occur naturally in human cells and are also present in foods such as organ meats, red meat, certain seafood and some alcoholic beverages.

Most uric acid dissolves in the blood, passes through the kidneys and leaves the body through urine. Measuring urinary uric acid over 24 hours provides information about how much uric acid the kidneys are excreting. A timed collection is used because uric acid output can vary during the day, and a single random urine sample may not accurately represent total daily excretion.

The test is commonly used when evaluating recurrent kidney stones, particularly when uric acid stones are suspected. It may also contribute to the assessment of gout, excessive uric acid production, reduced uric acid elimination and the effectiveness of treatment intended to control uric acid levels.

Benefits of the Test

• Measures the total quantity of uric acid excreted in urine over 24 hours.
• Supports assessment of patients with recurrent or suspected uric acid kidney stones.
• Helps distinguish increased uric acid production from reduced kidney elimination when interpreted with blood uric acid results.
• Contributes to the evaluation and management of gout and hyperuricaemia.
• May help doctors plan dietary changes, hydration strategies or uric acid-lowering treatment.
• Can be used to monitor the response to medicines that affect uric acid production or excretion.

Why Doctors Recommend This Test

A doctor may recommend this test for a person with recurrent kidney stones, crystals detected in urine, gout, persistently elevated blood uric acid or symptoms suggesting a urinary stone. Possible symptoms include severe pain in the side or lower back, pain spreading towards the groin, blood in urine, nausea, vomiting, painful urination or frequent urination.

The test may help determine whether an excessive amount of uric acid is entering the urine and increasing the likelihood of crystal or stone formation. Stone risk does not depend on uric acid alone. Urine volume, urine pH, hydration, diet and the concentration of other substances can also influence whether stones develop.

Doctors may also request urinary uric acid when investigating unusually high blood uric acid, monitoring gout treatment or evaluating patients receiving chemotherapy for certain cancers. Rapid breakdown of a large number of cells may release purines and substantially increase uric acid production. The result must therefore be interpreted together with the patient's medical history and other investigations.

Preparation Before Test

This test requires every urine sample passed during a specified 24-hour period to be collected in the container supplied or recommended by the laboratory. At the instructed starting time, empty the bladder and discard that first urine. Record the time. After this, collect every urine sample passed during the next 24 hours, including the final sample produced at the same time on the following day.

If even one urine sample is missed, spilled or not transferred to the collection container, inform the laboratory. An incomplete collection can produce a misleading result, and the collection may need to be restarted. Follow the laboratory's instructions about refrigeration, storage, preservatives and transportation. Do not add any unapproved substance to the container.

Inform the doctor about all medicines, nutritional supplements, recent contrast imaging and existing kidney conditions. Certain medicines and dietary factors may affect uric acid levels. Do not discontinue prescribed medicines or make major dietary changes unless instructed by the doctor. Follow the usual diet and fluid intake unless specific preparation instructions are provided.

Normal Reporting Time

The Uric Acid - 24 Hours Urine result is commonly available on the same day or within 24 hours after the completed collection reaches the laboratory. The 24-hour collection period itself must be completed before laboratory testing begins. Reporting time may vary according to specimen submission time, laboratory workflow, sample suitability and result verification requirements.

Who Should Take This Test?

This test may be appropriate for people with recurrent kidney stones, suspected uric acid stones, gout, elevated blood uric acid, crystals in urine or a family history of certain urinary stone disorders. It may also be requested for patients undergoing treatment that changes uric acid production or elimination.

The test should be performed when recommended by a healthcare professional. It is not a stand-alone screening test for everyone with joint pain or back pain. These symptoms have many possible causes, and the doctor will determine whether urinary uric acid measurement is relevant.

Detailed Information

Uric acid is produced mainly in the liver and intestines during purine metabolism. After entering the bloodstream, it is filtered by the kidneys. Some filtered uric acid is reabsorbed and some is secreted back into the urine. The final urinary result reflects the balance between uric acid production and kidney handling.

High urinary uric acid may occur with a purine-rich diet, increased breakdown of cells, certain blood disorders, some cancer treatments, gout or genetic and metabolic conditions. It may increase the risk of uric acid stones and may also contribute to calcium oxalate stone formation in some patients.

A low urinary uric acid result may occur when the kidneys excrete less uric acid, with certain medicines, reduced purine intake or some kidney-related conditions. A low value does not independently identify the cause of abnormal blood uric acid.

Results are generally expressed as the amount of uric acid excreted during 24 hours. Reference intervals vary between laboratories according to the analytical method, units, diet and patient population. The reference interval printed on the laboratory report should therefore be used for interpretation.

The result may be considered with serum uric acid, urine volume, urine pH, creatinine, kidney function tests and a comprehensive kidney stone evaluation. If a stone has been passed or removed, laboratory analysis of the stone may provide additional information about its composition.

An abnormal result does not by itself confirm gout or prove that a kidney stone is made of uric acid. The doctor should interpret it using symptoms, dietary history, medicine use, blood results, imaging findings and the completeness of the urine collection.