TTKG Calculator — Transtubular Potassium Gradient
Estimate the transtubular potassium gradient (TTKG) to judge whether the kidney is responding appropriately to a potassium disturbance.
When to use it
TTKG is a historical estimate. Urea recycling violates its assumptions, even when urine is concentrated and sodium delivery appears adequate. Do not use a TTKG threshold to diagnose aldosterone disorders; assess urine potassium excretion, medications, kidney function and the clinical context.
Formula
TTKG = (urine potassium x plasma osmolality) / (plasma potassium x urine osmolality).
Category
Acid-Base & Electrolytes
References
- Ethier JH et al. The transtubular potassium concentration in patients with hypokalemia and hyperkalemia. Am J Kidney Dis. 1990;15:309-15. PMID: 2321642
- Kamel KS et al. Intrarenal urea recycling leads to a higher rate of renal excretion of potassium: an hypothesis with clinical implications. Curr Opin Nephrol Hypertens. 2011;20:547-54. PMID: 21788894
- Kamel KS et al. Use of Urine Electrolytes and Urine Osmolality in the Clinical Diagnosis of Fluid, Electrolytes, and Acid-Base Disorders. Kidney Int Rep. 2021;6:1211-1224. PMID: 34013099
About NephroMind
This calculator is part of NephroMind, a free clinical decision-aid platform from the Arab Society of Nephrology and Renal Transplantation (ASNRT) — over 128 bedside nephrology calculators plus a renal drug-dosing database, coded by a practicing transplant nephrologist.