This quantitative laboratory test measures potassium ion excretion (K⁺) in a 24-hour urine collection. It is a key tool for assessing overall potassium balance in the body. Urine potassium excretion primarily reflects the activity of the hormone aldosterone on the distal renal tubules and the kidneys' ability to retain or excrete potassium, thus helping to differentiate between renal and non-renal causes of blood potassium imbalances.