Trans-tubular potassium gradient (TTKG) refers to the difference in the concentration of potassium ions between the urine collecting duct and the surrounding interstitium in the kidneys. TTKG is a vital factor in determining how much potassium is excreted in the urine and plays a critical role in regulating potassium balance in the body. There are several other terms that can be used interchangeably with TTKG, including urinary potassium to creatinine ratio (UK/PCR), fractional excretion of potassium (FEK), and tubular potassium secretion (TK), to name a few. Regardless of the terminology used, TTKG remains a fundamental aspect of renal physiology and homeostasis.