When is the measurement of the trans-tubular potassium gradient (TKKG) considered valid in hyperkalemia (high serum potassium level)?

Updated: Apr 09, 2020
  • Author: Eleanor Lederer, MD, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Measurement of the TTKG was initially considered superior to measurement of urine potassium alone for assessing the contribution of decreased renal excretion to hyperkalemia. However, it is important to recognize that the TTKG is valid for this purpose only if (1) the urine osmolality is greater than the serum osmolality—that is, the urine is concentrated relative to the serum—and (2) the urine sodium is greater than 20 mEq/L—that is, distal delivery of sodium is adequate for potassium excretion.

Furthermore, recent evidence suggesting that urea recycling may influence potassium secretion has cast some doubt on the utility of the TTKG. [61] One assumption inherent in the calculation of the TTKG is that the absorption of osmoles distal to the cortical collecting duct is negligible. If further studies suggest that urea transport can influence potassium handling, this test may have to be abandoned.

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