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Calculates the transtubular potassium gradient to assess renal potassium handling.
Clinical decision-support tool for qualified healthcare professionals. Results are not a diagnosis and should not replace professional clinical judgment.
The transtubular potassium gradient (TTKG) estimates the electrochemical gradient for potassium secretion in the cortical collecting duct. It is calculated as (urine K⁺ × plasma osmolality) / (plasma K⁺ × urine osmolality) and is intended to help distinguish renal from extrarenal potassium losses and to assess whether the kidney is appropriately secreting or retaining potassium. In the context of hyperkalemia, a TTKV < 8 suggests impaired distal tubular potassium secretion, pointing toward an intrinsic renal or hormonal cause (e.g., hypoaldosteronism, tubulointerstitial disease, ACE inhibitor/ARB use). A TTKV of 8–12 represents a normal renal potassium secretory response. A TTKV > 12 indicates enhanced distal potassium secretion, which may reflect extrarenal losses, mineralocorticoid excess, or other non-renal causes. Important interpretation limitations: The TTKV assumes that distal tubular flow rate is adequate and that urine osmolality is ≥ plasma osmolality, conditions that are not always met in clinical practice. Its physiological validity has been questioned because the underlying assumptions about urea recycling and Na⁺ reabsorption in the collecting duct may not hold uniformly. Diuretic use, especially loop or thiazide diuretics, can alter urine electrolyte composition and invalidate the calculation. TTKV should be interpreted alongside serum aldosterone, renin, acid-base status, and the full clinical picture. It is an adjunctive tool, not a definitive diagnostic test for potassium disorders.
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.
Transtubular potassium gradient = (urine potassium x plasma osmolality) / (plasma potassium x urine osmolality). It estimates renal potassium handling in the distal nephron.
Urine potassium in mmol/L, used in the numerator.
Plasma potassium in mmol/L, used in the denominator.
Urine osmolality in mOsm/kg, used in the denominator.
Plasma osmolality in mOsm/kg, used in the numerator.
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:
Expected Result: 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.