How this calculator works
TTKG is a historical calculation intended to adjust urinary potassium for water reabsorption. Its assumptions do not account adequately for urea recycling. Kamel and Halperin state that they no longer use it to assess dyskalaemia. This page reports the arithmetic for education and does not infer aldosterone activity or recommend treatment. Dilute urine creates an additional failure of the historical assumptions. The result is an estimate for information only and is not medical advice.
Formula
TTKG = (urine potassium / serum potassium) / (urine osmolality / serum osmolality). Potassium concentrations must share a unit, as must the two measured osmolalities.
Worked example
Urine potassium 40 and serum potassium 4 mmol/L, with urine osmolality 600 and serum osmolality 300 mOsm/kg, give 10 / 2 = 5. Urine potassium 80 with the other values unchanged gives 10.
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Frequently asked questions
Why is there no normal range?
The physiological assumptions can be wrong, so a universal diagnostic band would overstate the result.
Can I substitute calculated serum osmolality?
A measured paired osmolality is preferable for reproducing the historical method; calculated values add another assumption.
Can this identify a potassium treatment?
No. Clinical evaluation of potassium disorders requires other measurements and context.