Nephrology

Transtubular Potassium Gradient (TTKG)

Assesses renal potassium handling.

Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.

When to use

Use in hyper- or hypokalaemia to assess whether the renal response is appropriate (valid when urine osmolality > plasma and urine Na > 25).

Why use

It helps localise a potassium disorder to renal vs non-renal causes.

Critical actions

Only valid when urine osmolality exceeds plasma osmolality and urine sodium > 25 mmol/L. In hyperkalaemia a low TTKG (<5) suggests hypoaldosteronism; in hypokalaemia a high TTKG (>4) suggests renal loss.

Evidence & references

  1. Standard TTKG formula (urine K × plasma osmolality) / (plasma K × urine osmolality).

Related calculators

Calculated Serum OsmolalityEstimated osmolality from electrolytes.Fractional Excretion of Sodium (FENa)Distinguishes pre-renal from intrinsic AKI.

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