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Calculates the transtubular potassium gradient to assess renal potassium handling.
TTKG = (urinek * plasmaosmolality) / (plasmak * urineosmolality)
8–12
Interpret results together with the patient's clinical presentation.
Specialty
Internal MedicineCategory
NephrologyDifficulty
Basic
Estimated Time
30 seconds
Version
1.0
Last Updated
2026-08-06
Formula
Keywords
Normal Range
8–12
| Classification | Range |
|---|---|
Impaired K⁺ secretion | <8.1 |
Normal renal K⁺ response | 8–12 |
Enhanced K⁺ secretion | ≥12 |
Calculates the transtubular potassium gradient (TTKG) to assess renal potassium handling, primarily in the evaluation of hyperkalemia.
A TTKG of 8–12 reflects a normal renal potassium response. In hyperkalemia, a TTKG <8 suggests impaired distal potassium secretion (e.g., hypoaldosteronism or acute kidney injury), while a value >10 suggests intact aldosterone-mediated potassium secretion.
TTKG helps localize the cause of hyperkalemia to the kidney by evaluating distal potassium secretion, guiding further evaluation for hypoaldosteronism and tubular disorders.
A 70-year-old man with diabetic nephropathy has hyperkalemia (plasma K 5.0 mmol/L). Urine K is 40 mmol/L, urine osmolality 400 mOsm/kg, and plasma osmolality 300 mOsm/kg.
Inputs:
TTKG = (40 × 300) / (5.0 × 400) = 12,000 / 2,000 = 6.0 — impaired K⁺ secretion (<8), suggesting hypoaldosteronism; check aldosterone and renin levels.
A low TTKG (<8) in the setting of hyperkalemia suggests impaired distal potassium secretion, often due to hypoaldosteronism or distal tubular dysfunction.
TTKG remains a useful bedside tool, though some experts have questioned its physiological basis. It should be interpreted alongside other clinical data.
Disclaimer: This calculator is intended for educational and clinical decision support purposes only. TTKG should be interpreted within the full clinical context and not used alone.