🫘 Transtubular Potassium Gradient (TTKG)
Assess renal potassium handling in dyskalaemia with the transtubular potassium gradient.
Clinical takeaway
Hyperkalaemia: TTKG < 5–7 suggests impaired K excretion.
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When to use
Evaluate the kidney's potassium response in hyper- or hypokalaemia.
How it works
TTKG = (urine K / serum K) / (urine osm / serum osm). Requires urine osm > serum osm and adequate urine Na.
Key points
- Hyperkalaemia: TTKG < 5–7 suggests impaired K excretion.
- Hypokalaemia: TTKG > 4 suggests renal K wasting.
- Validity is debated; use as an adjunct only.
References
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Urine potassium | 40 mmol/L |
|---|---|
| Serum potassium | 5.5 mmol/L |
| Urine osmolality | 500 mOsm/kg |
| Serum osmolality | 290 mOsm/kg |
→TTKG4.2
- Hyperkalaemia：TTKG < 5–7 suggests impaired renal K excretion (e.g. hypoaldosteronism).
- Hypokalaemia：TTKG > 4 suggests renal potassium wasting.
- Validity：Urine osm > serum osm ✓
Frequently asked questions
- What is Transtubular Potassium Gradient (TTKG)?
- Assess renal potassium handling in dyskalaemia with the transtubular potassium gradient.
- How is Transtubular Potassium Gradient (TTKG) calculated? What is the core formula?
- TTKG = (urine K / serum K) / (urine osm / serum osm). Requires urine osm > serum osm and adequate urine Na.
- When is Transtubular Potassium Gradient (TTKG) used?
- Evaluate the kidney's potassium response in hyper- or hypokalaemia.
- What are the key clinical points for Transtubular Potassium Gradient (TTKG)?
- Hyperkalaemia: TTKG < 5–7 suggests impaired K excretion. Hypokalaemia: TTKG > 4 suggests renal K wasting. Validity is debated; use as an adjunct only.
- What are the limits and cautions when using Transtubular Potassium Gradient (TTKG)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is Transtubular Potassium Gradient (TTKG) calculated in practice? Can you show a worked example?
- Inputs: Urine potassium 40 mmol/L, Serum potassium 5.5 mmol/L, Urine osmolality 500 mOsm/kg, Serum osmolality 290 mOsm/kg → Result: TTKG 4.2（Hyperkalaemia: TTKG < 5–7 suggests impaired renal K excretion (e.g. hypoaldosteronism)., Hypokalaemia: TTKG > 4 suggests renal potassium wasting., Validity: Urine osm > serum osm ✓）