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Introduction ⬇

Uric acid is formed from the metabolic breakdown of nucleic acids composed of purines. Excessive uric acid relates to excessive dietary intake of purines or to endogenous uric acid production in certain disorders. Normally, one third of the uric acid formed is degraded by bacteria in the intestines.

This test evaluates uric acid metabolism in gout and kidney stone formation. Evaluation of excess uric acid excretion is important to aid in evaluating stone formation and nephrolithiasis. It also reflects the effects of treatment with uricosuric agents by measuring the total amount of uric acid excreted within a 24-hour period.

Normal Findings ⬆ ⬇

With normal diet: 250–750 mg/24 hr or 1.48–4.43 mmol/d

With purine-free diet: <400 mg/24 hr or <2.48 mmol/d

With high-purine diet: <1000 mg/24 hr or <5.90 mmol/d

Procedure ⬆ ⬇

  1. Properly label a 24-hour urine container to which the appropriate preservative has been added. Label with the patient’s name, date and time of collection, and test(s) ordered.

  2. Follow general instructions for 24-hour urine collection (see Long-Term, Timed Urine Specimen [2-Hour, 24-Hour]).

  3. Record exact starting and ending times on the specimen container and in the patient’s healthcare record.

  4. When collection is completed, send the specimen to the laboratory.

Clinical Implications ⬆ ⬇

  1. Increased urine uric acid (uricosuria) occurs in:

    1. Nephrolithiasis (primary gout)

    2. Chronic myelogenous leukemia (secondary nephrolithiasis)

    3. Polycythemia vera

    4. Lesch–Nyhan syndrome

    5. Wilson disease

    6. Viral hepatitis

    7. Sickle cell anemia

    8. High uric acid concentration in urine with low urine pH may produce uric acid stones in the urinary tract. (These patients do not have gout.)

  2. Decreased urine uric acid is found in:

    1. CKD

    2. Xanthinuria

    3. Folic acid deficiency

    4. Lead toxicity

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for 24-hour urine collection (including the need to refrigerate or place the specimen on ice), and interfering factors. Written instructions can be helpful.

  2. Encourage food and fluids. In some situations, a diet high or low in purines may be ordered during and before specimen collection.

  3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Have the patient resume a normal diet.

  2. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the prescribed treatment and possible need for further testing.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. Many drugs increase uric acid levels, including:

    1. Salicylates (aspirin) and other nonsteroidal anti-inflammatory drugs (NSAIDs)

    2. Diuretics

    3. Vitamin C (ascorbic acid)

    4. Warfarin

    5. Cytotoxic drugs used to treat lymphoma and leukemia (see Appendix E)

  2. Other factors increasing uric acid urine levels include:

    1. X-ray contrast media

    2. Strenuous exercise

    3. Diet high in purines (e.g., kidney, sweetbreads) (see Chapter 6)

  3. Allopurinol decreases uric acid levels (see Appendix E)