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Introduction ⬇

The principal substances formed by the adrenal medulla and excreted in urine are epinephrine, norepinephrine, metanephrine, and normetanephrine. These substances contain a catechol nucleus together with an amine group and therefore are referred to as catecholamines. Most of these hormones are changed into metabolites, the principal one being 3-methoxy-4-hydroxymandelic acid, known as VMA.

VMA is the primary urinary metabolite of the catecholamine group. It has a urine concentration 10–100 times greater than the concentrations of the other amines. It is also fairly simple to detect; methods used for catecholamine determination are much more complex.

This 24-hour urine test of adrenomedullary function is done primarily when pheochromocytoma, a tumor of the chromaffin cells of the adrenal medulla, is suspected in a patient with hypertension.

The assay for pheochromocytoma is most valuable when a urine specimen is collected during a hypertensive episode. Because a 24-hour urine collection represents a longer sampling time than a symptom-directed serum sample, the 24-hour urine test may detect a pheochromocytoma missed by a single blood level determination.

Normal Findings ⬆ ⬇

Adults

VMA: <7 mg/24 hr or <35 μmol/d

Catecholamines (total): <100 μg/d or <505 nmol/d

Epinephrine: 0–20 μg/24 hr or 0–101 nmol/d

Metanephrine: 74–297 μg/24 hr or 374–1500 nmol/d

Norepinephrine: <100 μg/24 hr or <505 nmol/d

Normetanephrine: 105–354 μg/24 hr or 530–1787 nmol/d

Dopamine: 65–400 μg/24 hr or 328–2020 nmol/d

Children’s levels are different from those of adults. Check with your laboratory for values in children.

Procedure ⬆ ⬇

  1. Properly label (patient’s name, date and time of collection, and test[s] ordered) a 24-hour container with acid preservative (20 mL of HCl, 6 mol/L) and refrigerate the container or keep it on ice. Stable up to 14 days.

  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 of the collection on the specimen container and in the patient’s healthcare record.

  4. Send the specimen to the laboratory.

Clinical Implications ⬆ ⬇

  1. Increased urine VMA occurs as follows:

    1. High levels in pheochromocytoma

    2. Slight to moderate elevations in:

      1. Neuroblastoma

      2. Ganglioneuroma

      3. Ganglioblastoma

      4. Carcinoid tumor (some cases)

  2. Increased urine catecholamines are found in:

    1. Pheochromocytoma

    2. Neuroblastomas

    3. Ganglioneuromas

    4. Acute myocardial infarction

    5. Hypothyroidism

    6. Diabetic acidosis

    7. Long-term manic or depressive episodes

  3. Decreased urine catecholamines are found in:

    1. Diabetic neuropathy

    2. Parkinson disease

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for 24-hour urine collection, and interfering factors. Written instructions can be helpful, especially regarding restricted foods.

  2. Explain diet and drug restrictions. Diet restrictions vary among laboratories, but coffee, tea, bananas, cocoa products, vanilla products, and aspirin are always excluded for 3 days (2 days before and 1 day during specimen collection).

  3. Many laboratories require that all medications be discontinued for 1 week before specimen collection. Obtain healthcare provider’s approval.

  4. Encourage adequate rest, food, and fluids.

  5. Stress, strenuous exercise, and smoking should be avoided during the test.

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

Posttest Patient Care

  1. Have the patient resume a normal diet, medications, and activity.

  2. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel patient regarding abnormal findings.

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

Interfering Factors ⬆

  1. Increased urine VMA and catecholamines are caused by:

    1. Hypoglycemia—for this reason, the test should not be scheduled while the patient is NPO (nothing by mouth).

    2. Many foods, such as the following:

      1. Caffeine-containing products (e.g., tea, coffee, cocoa, carbonated drinks)

      2. Vanilla

      3. Fruit, especially bananas

      4. Licorice

    3. Many drugs cause increased VMA levels, especially reserpine, α-methyldopa, levodopa, monoamine oxidase inhibitors, sinus and cough medicines, bronchodilators, and appetite suppressants.

    4. Exercise, stress, smoking, and pain cause physiologic increases of catecholamines.

    5. Heavy alcohol intake increases catecholamine levels.

  2. Falsely decreased levels of VMA and catecholamines are caused by:

    1. Alkaline urine

    2. Uremia (causes toxicity and impaired excretion of VMA)

    3. Radiographic contrast agents—for this reason, an intravenous pyelogram should not be scheduled before a VMA test.

    4. Certain drugs (see Appendix E)