Home :: Potassium Test

Potassium - Deficiency Test

The potassium test is a quantitative test that measures urine levels of potassium, a major intracellular cation that helps regulate acid-base balance and neuromuscular function. Potassium imbalance may cause such signs and symptoms as muscle weakness, nausea, diarrhea, confusion, hypotension, and electrocardiogram changes; severe imbalance may lead to cardiac arrest.

Most commonly, a serum potassium test is performed to detect hyperkalemia (abnormally high levels) or hypokalemia (abnormally low levels). A urine potassium test may be performed to evaluate hypokalemia when a history and physical examination fail to uncover the cause. If results suggest a renal disorder, additional renal function tests may be ordered.

Purpose

• To determine whether hypokalemia is caused by renal or extrarenal disorders

Patient preparation

• Explain to the patient that this test evaluates his kidney function.
• Advise him that no special dietary restrictions are necessary.
• Tell him that the test requires urine collection over a 24-hour period.
• If the specimen is to be collected at home, teach him the correct collection technique.

Procedure and posttest care

• Collect the patient's urine over a 24hour period.
• Administer potassium supplements and monitor serum levels as appropriate.
• Provide dietary supplements and nutritional counseling as necessary.
• Replace volume loss with I.V. or oral fluids as necessary.
• Resume administration of drugs withheld during the test.

Precautions

• Tell the patient not to contaminate the specimen with toilet tissue or stool.
• Refrigerate the specimen or place it on ice during the collection period.
• Send the specimen to the laboratory immediately after collection or refrigerate it.

Reference values

Normal potassium excretion in adults is 25 to 125 mEq/24 hours, or 25 to 125 mmol/24 hours. In children, normal excretion is 22 to 57 mmol/24 hours.

Abnormal findings

In a patient with hypokalemia, potassium concentration less than 10 mEq/L suggests normal renal function, indicating that potassium loss is most likely the result of a GI disorder such as malabsorption syndrome.

In a patient with hypokalemia lasting more than 3 days, urine potassium concentration above 10 mEq/L indicates renal loss of potassium. These losses may result from such disorders as aldosteronism, renal tubular acidosis, or chronic renal failure. However, extrarenal disorders, such as dehydration, starvation, Cushing's disease, or salicylate intoxication, may also elevate urine potassium levels.

Interfering factors

• Contamination of the specimen with toilet tissue or stool
• Failure to send the specimen to the laboratory immediately or to refrigerate it
• Ammonium chloride, thiazide diuretics, and acetazolamide