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Introduction ⬇

Potassium (K) acts as a part of the body’s buffer system and serves a vital function in the body’s overall electrolyte balance. Because the kidneys cannot completely conserve potassium, this balance is regulated by the excretion of potassium through the urine. It takes the kidney 1–3 weeks to conserve potassium effectively.

This test provides insight into electrolyte balance by measuring the amount of potassium excreted in 24 hours. This measurement is useful in the study of renal and adrenal disorders and water and acid–base imbalances. An evaluation of urinary potassium can be helpful in determining the origin of abnormal potassium levels. Urine potassium values of <20 mEq/L (or <20 mmol/L) are associated with nonrenal conditions, whereas values of >20 mEq/L (or >20 mmol/L) are associated with kidney-related causes.

Normal Findings ⬆ ⬇

Adult: 25–125 mEq/24 hr or 25–125 mmol/d

Child: 10–60 mEq/24 hr or 10–60 mmol/d

Values are diet dependent.

The transtubular potassium gradient (TTKG) is an index that reflects potassium conservation by the kidneys.

TTKG = urine K/plasma K ÷ urine osmolality/plasma osmolality

Normal TTKG = 8–9 is seen in a normal diet.

TTKG >10 is seen with high potassium intake and more excretion by the kidneys.

TTKG <3 is seen with low potassium intake and less excretion by the kidneys.

TTKG <7 is seen with hyperkalemia and may indicate mineralocorticoid deficiency.

Procedure ⬆ ⬇

  1. Label a 24-hour urine container properly with the patient’s name, date and time of collection, and test(s) ordered.

  2. Refrigerate the urine container or keep it on ice during the collection.

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

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

  5. Transfer the specimen to the laboratory for proper storage.

  6. A random urine potassium determination may be done.

Clinical Implications ⬆ ⬇

  1. Increased urine potassium occurs in:

    1. Primary kidney diseases

    2. Diabetic and renal tubule acidosis

    3. Chronic kidney disease (CKD)

    4. Starvation (onset)

    5. Primary and secondary aldosteronism

    6. Cushing syndrome

    7. Onset of metabolic alkalosis

    8. Fanconi syndrome

    9. Bartter syndrome

  2. Decreased urine potassium occurs in:

    1. Addison disease

    2. Severe kidney disease (e.g., pyelonephritis, glomerulonephritis)

    3. In patients with potassium deficiency, regardless of the cause, the urine pH tends to decrease. This occurs because hydrogen ions are released in exchange for sodium ions, given that both potassium and hydrogen are excreted by the same mechanism.

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.

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

Clinical Alert

  1. Because electrolytes and water balance are so closely related, determine the patient’s state of hydration by checking and recording daily weights, accurate intake and output of fluids, and observations about skin turgor, the appearance of the tongue and mucous membranes, and the appearance of the urine.

  2. Observe for signs of muscle weakness, tremors, changes in electrocardiographic tracings, and dysrhythmias. The degree of hypokalemia or hyperkalemia at which these symptoms occur varies with each person.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Monitor appropriately for signs and symptoms of electrolyte imbalances and kidney disorders.

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

Interfering Factors ⬆

  1. Increased urinary potassium is associated with:

    1. Acetazolamide and other diuretics

    2. Cortisone

    3. Ethylenediaminetetraacetic acid (EDTA) anticoagulant

    4. Penicillin, carbenicillin

    5. Thiazides

    6. Licorice

    7. Sulfates (see Appendix E)

  2. Decreased urinary potassium is associated with:

    1. Amiloride

    2. Diazoxide

    3. Intravenous glucose infusion (see Appendix E)

Clinical Alert

In the presence of excessive vomiting or gastric suctioning, the resulting alkalosis maintains urinary potassium excretion at levels inappropriately high for the degree of actual potassium depletion that occurs