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Transtubular Potassium Gradient (TTKG), a standard published formula used to assess renal potassium handling (West ML et al., "New clinical approach to evaluate disorders of potassium excretion", Mineral and Electrolyte Metabolism, 1986): TTKG = (Urine K x Serum osmolality) / (Serum K x Urine osmolality). Pure arithmetic on four lab values you provide, with no interpretation of the result beyond the calculation. For general reference and educational purposes only — not a medical diagnosis. Consult a doctor for actual electrolyte assessment.
How it works
Enter urine potassium, serum osmolality, serum potassium, and urine osmolality. The tool applies the standard TTKG formula.
- Enter urine potassium (mEq/L).
- Enter serum osmolality (mOsm/kg).
- Enter serum potassium (mEq/L).
- Enter urine osmolality (mOsm/kg).
- Click Calculate to see your results.
Examples
Urine K 40, Serum osm 290, Serum K 4.0, Urine osm 400
TTKG = (40 x 290) / (4.0 x 400) = 11600 / 1600 = 7.25.
Who should use it
- Reviewing a potassium disorder work-up alongside a doctor.
- Nephrology education about renal potassium handling.
Industry applications
- Nephrology reference
- Endocrinology and critical care education
Advantages
- Long-published, widely taught formula.
- Uses routinely available lab values.
Limitations
- Its underlying assumptions have been questioned in more recent nephrology literature.
- A single-point calculation — not a complete clinical picture on its own.
Common mistakes to avoid
- Calculating TTKG when urine osmolality is lower than serum osmolality, a setting where the formula's assumptions do not hold.
- Mixing up which values are urine versus serum.
Best practices
- Check that urine osmolality exceeds serum osmolality before relying on a TTKG result, per commonly cited nephrology caveats.
Tips
- TTKG is typically interpreted alongside aldosterone status and the overall clinical context, not as a standalone number.