Transtubular potassium gradient (TTKG)
Estimates potassium secretion in the cortical collecting duct.
Inputs
0 of 4mEq/L
mEq/L
mOsm/kg
mOsm/kg
When to use
- Unexplained hypokalemia or hyperkalemia.
Pearls and pitfalls
- Valid only when urine osmolality exceeds plasma and urine sodium is above 25 mEq/L.
- Its originators later advised against relying on it; the urine K/Cr ratio is an alternative.
Why use
Still widely taught and requested; shown with its validity checks.
TTKG = (urine K ÷ plasma K) ÷ (urine osm ÷ plasma osm)