transtubular potassium gradient

trans-tubular potassium gradient

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The transtubular potassium gradient (TTKG) is a formula used to assess renal handling of potassium. It adjusts the urinary potassium for the concentrating effects that occur in the collecting tubule, where water is removed from the urine. A high TTKG suggests that the kidney is wasting potassium, which may be appropriate (in the setting of hyperkalemia) or inappropriate (in the setting of hypokalemia).

A high TTKG in the setting of hypokalemia might suggest hyperaldosteronism or pseudohyperaldosteronism (e.g. Cushing's syndrome, particularly in the setting of traditional licorice ingestion, or a tubular abnormality like Liddle's syndrome).

A low TTKG in the setting of hyperkalemia might suggest a type IV renal tubular acidosis.

transtubular potassium gradient = (urine k/serum k)/(urine osm/serum osm))
Multiply by 100 for percentage.


  1. West et al. New clinical approach to evaluate disorders of potassium excretion. Miner Electrolyte Metab (1986) vol. 12 (4) pp. 234-8