The Potassium test is a blood test that measures the concentration of potassium, the most abundant intracellular cation in the human body, in the blood serum. Approximately 98 percent of the body's total potassium is stored within cells, particularly in muscle, liver, and red blood cells, with only two percent circulating in the extracellular fluid and bloodstream. This narrow extracellular concentration is maintained within a very tight physiological range through the coordinated actions of the sodium-potassium ATPase pump, renal tubular regulation under the influence of aldosterone, acid-base status, and insulin, because even small deviations from the normal range have profound consequences for cardiac electrical conduction, neuromuscular function, and cellular metabolism.
Potassium plays an indispensable role in maintaining the resting membrane potential of excitable cells including cardiac myocytes, skeletal muscle fibres, and neurons. The ratio of intracellular to extracellular potassium concentration determines cellular excitability, and disruptions to this ratio cause the characteristic clinical manifestations of potassium disorders. Hypokalaemia, or low serum potassium, increases cellular excitability and predisposes to cardiac arrhythmias, muscle weakness, and paralytic ileus, while hyperkalaemia, or high serum potassium, decreases excitability and causes potentially fatal cardiac conduction abnormalities including ventricular fibrillation and asystole.
In India, potassium disorders are encountered across virtually every clinical specialty. Hypokalaemia is particularly prevalent in patients with chronic diarrhoeal illness, malnutrition, diuretic use, and hyperaldosteronism, while hyperkalaemia is a common and potentially life-threatening complication of chronic kidney disease, diabetic nephropathy, and the widespread use of renin-angiotensin-aldosterone system blocking medications. The test is performed on a small blood sample drawn from a vein and completed in under five minutes.