🫘 Transtubular Potassium Gradient (TTKG)
Assess renal potassium handling in dyskalaemia with the transtubular potassium gradient.
Transtubular Potassium Gradient (TTKG)
Urine potassium (mmol/L)
Serum potassium (mmol/L)
Urine osmolality (mOsm/kg)
Serum osmolality (mOsm/kg)
When to use
Evaluate the kidney's potassium response in hyper- or hypokalaemia.
How it works
TTKG = (urine K / serum K) / (urine osm / serum osm). Requires urine osm > serum osm and adequate urine Na.
Key points
- Hyperkalaemia: TTKG < 5–7 suggests impaired K excretion.
- Hypokalaemia: TTKG > 4 suggests renal K wasting.
- Validity is debated; use as an adjunct only.
References
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.