When hypokalemia occurs, it is important to determine whether the loss of potassium is extrarenal or renal. Diagnostic criteria for renal potassium loss: 1. 24-hour urinary potassium excretion rate, if in hypokalemia (e.g. blood potassium <3.5mmol/L), 24-hour urinary potassium is still >25mmol/day, it proves to be a renal potassium loss. 2. 24-hour urinary potassium concentration, if blood potassium is <3.5mmol/L and potassium concentration is still >20mmol/L, it also supports the diagnostic criteria for renal potassium loss. 3. Because 24-hour urine potassium retention is difficult and complicated, some patients cannot understand it correctly, sometimes they choose to measure the ratio of urine potassium to creatinine in a single urine, if the ratio of urine potassium to creatinine is significantly greater than the normal range, it also supports the diagnosis of renal potassium loss. 4. The decision is based on the trans tubular potassium gradient, or TTKG, if it is >6, it supports the diagnosis of renal potassium loss.