Transtubular Potassium Gradient (TTKG)
Estimates aldosterone activity by assessing potassium secretion in the collecting duct. Used to differentiate causes of hyperkalaemia (renal vs extra-renal) and hypokalaemia.
Score interpretation
TTKG < 4 in hyperkalaemia: Inappropriate renal potassium retention — suggests hypoaldosteronism or aldosterone resistance (Type 4 RTA).
→ Consider: Addison's disease, hyporeninism (diabetes, NSAIDs), ACEi/ARB/spironolactone/trimethoprim effect. Investigate aldosterone and renin. Stop offending drugs.
TTKG 4–7: Borderline. Interpretation requires clinical context.
→ Correlate with serum potassium level and clinical presentation. Repeat after stopping potassium-retaining drugs.
TTKG > 7 in hyperkalaemia: Appropriate aldosterone-mediated potassium excretion. Extra-renal source of potassium load.
→ Investigate extra-renal causes: rhabdomyolysis, haemolysis, tissue necrosis, excessive potassium intake, pseudohyperkalaemia.
Interpretation bands for the TTKG. Apply clinical judgement and local guidance.
References
- Ethier JH, et al. The transtubular potassium concentration in patients with hypokalemia and hyperkalemia. Am J Kidney Dis. 1990;15(4):309–315.
Related
Curated clinical cross-links plus same-class fallbacks.
- Spironolactone · Aldosterone antagonist (potassium-sparing diuretic)
- Spironolactone (Ascites / Cirrhosis) · Aldosterone Antagonist / Potassium-Sparing Diuretic
- Potassium Chloride (IV) · Electrolyte — Potassium Supplement
- Amiloride hydrochloride · Potassium-sparing diuretic (epithelial Na+ channel blocker)
- Co-amilofruse · Loop diuretic + potassium-sparing
- Co-amilozide · Thiazide + potassium-sparing
- Hyperkalaemia Management · UK Kidney Association Guidelines 2020; NICE CKD Guidelines
- Rhabdomyolysis · Renal Association 2018; UpToDate 2024
- Hypocalcaemia (Adult) · Society for Endocrinology
- SIADH (Endocrine Perspective) · European Hyponatraemia Guidelines 2014
- Hepatorenal Syndrome · EASL 2018; ICA 2015
- Acute Kidney Injury (AKI) · KDIGO 2012 / NICE AKI 2019
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.