Potassium (K)

Overview

Potassium (K) measures the concentration of this essential intracellular cation in blood, primarily in the extracellular fluid, where it is tightly regulated by the kidneys and influenced by acid–base balance and hormonal activity. Potassium is critical for maintaining the resting membrane potential of excitable cells, including cardiac myocytes, skeletal muscle, and neurons, and thus plays a central role in cardiac conduction and muscle contraction. Low serum potassium (hypokalemia) can cause arrhythmias, muscle weakness, and fatigue, whereas high levels (hyperkalemia) can lead to life‑threatening cardiac arrhythmias and sudden cardiac arrest. Clinically, serum potassium is a routine electrolyte in basic metabolic panels used to assess electrolyte status, guide correction of imbalances, and monitor patients on diuretics, ACE inhibitors, or other potassium‑modifying drugs.

Clinical Use Cases

  • Assessing electrolyte imbalance in dehydration, vomiting, diarrhea, or diuretic use.
  • Evaluating and monitoring therapy for hypokalemia or hyperkalemia (e.g., in heart failure, renal disease, or adrenal disorders).
  • Supporting workup of arrhythmias, muscle weakness, or unexplained ECG changes.
  • Monitoring patients on medications that alter potassium (e.g., thiazide or potassium‑sparing diuretics, ACE inhibitors, ARBs, NSAIDs, heparin).

Specimen Types

  • Serum (most commonly used).
  • Plasma (heparinized plasma; note that hemolysis can falsely elevate potassium).

Measurement Methods

  • Ion‑selective electrode (ISE) on automated clinical chemistry analyzers (most common method).
  • Flame photometry (older method, used in some reference or specialized labs).

Test Preparation and Influencing Factors

  • Fasting is not required, but consistent timing is recommended for serial monitoring.
  • Hemolysis of the sample, prolonged tourniquet time, and vigorous fist‑clenching during venipuncture can falsely elevate serum potassium.
  • Insulin, beta‑agonists, and alkalosis drive potassium into cells and transiently lower serum levels, whereas acidosis and tissue breakdown (e.g., rhabdomyolysis) increase extracellular potassium.
  • Certain medications (e.g., potassium‑sparing diuretics, ACE inhibitors, spironolactone, NSAIDs, digoxin) and renal dysfunction strongly influence potassium concentration.

Synonyms

  • Serum potassium.
  • Potassium, K⁺.
  • Potassium level (general clinical term).

Further Reading