The transtubular K gradient test (TTKG) is employed to measure renal potassium secretion through the cortical collecting duct, providing an indirect evaluation of mineralocorticoid bioactivity in individuals with hypokalemia or hyperkalemia. Healthcare professionals utilize this test to assess the adequacy of the renal response to hyperkalemia or hypokalemia and to gauge the appropriateness of renal K+ excretion in cases of abnormal serum K+ concentration.