What is transtubular potassium gradient (TTKG) and how can it be used in diagnosis of hyperkalemia?
TTKG is a measurement of the potassium gradient between urine in the distal nephron (cortical collecting tubule) and the peritubular capillaries after correcting for changes in urine osmolality. TTKG = Urine K + / Serum K + × Serum Osmolality/Urine Osmolality
It was originally proposed that a TTKG >10 suggests normal aldosterone secretion and action and a TTKG <5 to 7 was thought to suggest aldosterone deficiency or resistance. Use of TTKG in the evaluation of patients with hyperkalemia is no longer recommended.