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Transtubular K⁺ Gradient (TTKG)
Assesses mineralocorticoid activity in potassium disorders
Laboratory Inputs
Required (1–300)
Required (1–10)
Required (50–1400)
Required (250–380)
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TTKG
| Context | TTKG | Interpretation |
|---|---|---|
| Normal diet | 8–9 | Normal aldosterone activity |
| Hyperkalemia | < 5 | Hypoaldosteronism or aldosterone resistance |
| Hyperkalemia | > 7 | Extra-renal cause of hyperkalemia |
| Hypokalemia | < 2 | Extra-renal K loss (GI losses, poor intake) |
| Hypokalemia | > 4 | Renal K wasting (hyperaldosteronism, diuretics) |
TTKG = (UK / PK) / (Uosm / Posm)
Prerequisite: Uosm > Posm (urine must be hypertonic to plasma)
Reflects cortical collecting duct K secretion relative to aldosterone activity
Prerequisite: Uosm > Posm (urine must be hypertonic to plasma)
Reflects cortical collecting duct K secretion relative to aldosterone activity
Limitations: TTKG validity requires urine osmolality > plasma osmolality. Reliability questioned in some studies. Best used as one component of the workup alongside aldosterone/renin levels. Does not apply in acute renal failure with anuria/oliguria.
