The transtubular potassium gradient estimates the electrochemical gradient for potassium secretion at the distal potassium secretory site and has been proposed as an estimate for the driving force for tubular potassium secretion. The test can be used in the diagnosis of hypoaldosteronism.


transtubular potassium gradient =

= ((urine potassium in mEq/L) / (plasma potassium in mEq/L)) / ((urine osmolality in mOsm per kg H2O) / (plasma osmolality in mOsm per kg H2O))



• A very low values for TTKG can be seen with: potassium sparing diuretics, agents which block aldosterone effects, water diuresis, hypokalemia, instrinsic renal disease, diabetic ketoacidosis, hyperglycemic hyperosmolar syndrome, and very slow delivery of sodium to the cortical distal nephron



• The calculation invalid if urine is less than iso-osmolal.

• At very high urine flow rates the TTKG may falsely indicate low or defective potassium secretion because of insufficient time for equilibrium to be established in the distal nephron.


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