Transtubular Potassium Gradient at CCD

 

TTKG = (UrineK / SerumK) / (UrineOsm / SerumOsm)

 

Input:
 

Urine K		mEq/L mmol/L
Serum K		mEq/L mmol/L
Urine Osm		mOsm/dL mOsm/kg
Serum Osm		mOsm/dL mOsm/kg

 

Result:
 

TTKG		# index logit none number points score
Decimal Precision   0 1 2 3

 

Notes

• The transtubular potassium gradient in the cortical collecting duct is an index reflecting conservation of potassium. A normal TTKG in normal subjects on normal diets is 8-9.
• With a potassium load the TTKG may rise to 11.
• In the face of Hyperkalemia, a low TTKG (<7) may indicate hypoaldosteronism.
• Without other disease, hypokalemia should produce a TTKG <3 (some authors say TTKG <2.) The expected TTKG in hyperkalemia is >10.

 

References

1. 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: 3762510
2. Ethier JH, Kamel KS, Magner PO, et al. The transtubular potassium concentration in patients with hypokalemia and hyperkalemia. Am J Kidney Dis. 15:309,1990. PubMed ID: 2321642