Trans-Tubular Potassium Gradient Calculator

TTKG Equation:

\[ TTKG = \frac{U_K / P_K}{U_{Osm} / P_{Osm}} \]

Urine Potassium (U_K):

mmol/L

Plasma Potassium (P_K):

mmol/L

Urine Osmolality (U_Osm):

mOsm/kg

Plasma Osmolality (P_Osm):

mOsm/kg

Trans-Tubular Potassium Gradient (TTKG):

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1. What is Trans-Tubular Potassium Gradient?

The Trans-Tubular Potassium Gradient (TTKG) is a calculated parameter that estimates the potassium concentration gradient between the tubular fluid and peritubular capillaries in the cortical collecting duct. It helps differentiate between renal and extrarenal causes of potassium disorders.

2. How Does the Calculator Work?

The calculator uses the TTKG equation:

\[ TTKG = \frac{U_K / P_K}{U_{Osm} / P_{Osm}} \]

Where:

\( U_K \) — Urine potassium concentration (mmol/L)
\( P_K \) — Plasma potassium concentration (mmol/L)
\( U_{Osm} \) — Urine osmolality (mOsm/kg)
\( P_{Osm} \) — Plasma osmolality (mOsm/kg)

Explanation: The TTKG corrects for water reabsorption in the collecting duct by accounting for the urine-to-plasma osmolality ratio, providing a more accurate assessment of potassium handling.

3. Clinical Importance of TTKG

Details: TTKG is particularly useful in evaluating hyperkalemia and hypokalemia. It helps determine whether the kidneys are appropriately responding to potassium imbalances and can guide diagnostic workup and treatment decisions.

4. Using the Calculator

Tips: Enter all four parameters in their respective units. Ensure values are positive and measured simultaneously for accurate results. The calculator provides the TTKG as a unitless ratio.

5. Frequently Asked Questions (FAQ)

Q1: What is the normal range for TTKG?
A: Normal TTKG ranges from 6-12 in individuals with normal potassium balance, but interpretation depends on the clinical context and serum potassium levels.

Q2: How is TTKG used in hyperkalemia?
A: In hyperkalemia, TTKG <5-7 suggests inadequate renal potassium excretion, while TTKG >10 suggests appropriate renal response to hyperkalemia.

Q3: How is TTKG used in hypokalemia?
A: In hypokalemia, TTKG >2 suggests renal potassium wasting, while TTKG <2 suggests extrarenal causes or appropriate renal conservation.

Q4: What are the limitations of TTKG?
A: TTKG assumes urine osmolality > plasma osmolality and may be unreliable with very low urine osmolality. It's also affected by urine flow rate and medications.

Q5: When should TTKG not be used?
A: TTKG is unreliable with urine osmolality less than plasma osmolality, in the presence of osmotic diuresis, or when urine sodium is very low.