Transtubular potassium gradient (TTKG)
Transtubular potassium gradient = (urine k/serum k)/(urine osm/serum osm))
Urine potassium (Urine
Plasma potassium (Plasma k):
Urine osmolality (Urine Osm):
Serum osmolality (Serum Osm):
Is the urine sodium (UNa) > 25 mEq/L? :
Transtubular potassium gradient (TTKG) -
The TTKG reflects the conservation of potassium in the cortical
collecting ducts (CCD) of the kidneys. It also estimates the ratio
of potassium in the lumen of the CCD to that in the peritubular
capillaries which may be useful in diagnosing the causes of
hyperkalemia or hypokalemia.
TTKG values less than 6 suggests a renal cause of hyperkalemia
(aldosterone deficiency or lack of response).
TTKG values greater than 6 suggests an extrarenal cause of
hyperkalemia such as increased potassium intake, hemolysis, acidosis,
If TTKG is less than 6 with a normal serum aldosterone -->
possible renal tubular deficit. Other scenarios: low
aldosterone, nml serum renin --> hypoaldosteronism. Low aldosterone
and low serum renin --> hyporeninemic hypoaldosteronism.
Typical TTKG in a normal person on a normal diet is 8-9.
or high potassium intake, more potassium should be excreted in the urine and
the TTKG should be above 10.
Low levels (<7) during hyperkalemia may indicate
mineralocorticoid deficiency, especially if accompanied by hyponatremia and
high urine Na.
During potassium depletion or hypokalemia, the TTKG should fall to less than
3, indicating appropriately reduced urinary excretion of potassium.
TTKG > 2 and hypokalemia --> renal loss.
Useful in gauging the correctness of renal K excretion during
disorders in serum potassium
Index of potassium secretory activity in the distal tubule
(gauges renal potassium
secretion by the cortical collecting duct (CCD), indirectly assessing
mineralocorticoid activity in patients who have elevated or low potassium
Choi MJ, Ziyadeh
FN. The utility of the transtubular potassium
gradient in the evaluation of hyperkalemia. J Am Soc Nephrol 19:
424–426, 2008. PMID 18216310.
Ethier JH, Kamel KS, Magner PO, Lemann J, Halperin ML (April 1990). "The
transtubular potassium concentration in patients with hypokalemia and
hyperkalemia". Am. J. Kidney Dis. 15 (4): 309–15,1990. PMID 2321642
West ML, Marsden PA, Richardson RM, et. al., New clinical approach to
evaluate disorders of potassium excretion, Mineral Electrolyt Metab,
12:234,1986., PubMed ID number 3762510