TTKG Calculator: Transtubular Potassium Gradient

Your details

Plasma or serum potassium concentration. Normal range: 3.5 to 5.0 mmol/L.
mmol/L
Spot urine potassium concentration from a random urine sample. Must be a valid urine sample (urine osmolality >= 300 mOsm/kg).
mmol/L
Measured serum osmolality. Normal range: 275 to 295 mOsm/kg. Can be estimated as 2 x Na + glucose/18 + BUN/2.8.
mOsm/kg
Measured urine osmolality. Must be >= 300 mOsm/kg for the TTKG to be valid. Values below this indicate insufficient antidiuretic hormone effect for reliable assessment.
mOsm/kg
Optional: used only to flag validity. TTKG is unreliable when urine Na is below 25 mmol/L because sodium delivery to the collecting duct affects potassium secretion.
mmol/L
Select the clinical context to tailor the interpretation. TTKG thresholds differ between hypo- and hyperkalemia.
TTKGPossible renal K+ wasting
3.02

Transtubular potassium gradient: the estimated K+ concentration ratio across the collecting duct

Urine/serum K+ ratio4.69
Urine/serum osmolality ratio1.552
Validity checkValid: prerequisites met
InterpretationTTKG >= 3 with hypokalemia: inappropriately elevated K+ excretion. Suggests renal potassium wasting (hyperaldosteronism, Bartter/Gitelman syndrome, diuretic use, Liddle syndrome).
3.02
Very low<3Low3-5Mid5-10High10+

TTKG is 3.02 (hypokalemia context).

  • Your TTKG is 3.02, reflecting the estimated potassium concentration ratio across the cortical collecting duct corrected for water reabsorption.
  • An elevated TTKG in the setting of hypokalemia indicates the kidneys are inappropriately wasting potassium. Mineralocorticoid excess (primary or secondary hyperaldosteronism) is high on the differential.
  • TTKG is a screening index, not a definitive test. Confirm with aldosterone, renin, cortisol, and 24-hour urine K+ measurements as clinically indicated.

Next stepIf TTKG indicates renal wasting, measure plasma aldosterone and renin ratio to differentiate primary from secondary hyperaldosteronism.

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