Transtubular 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

Transtubular Potassium Gradient (TTKG):

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1. What is Transtubular Potassium Gradient?

The Transtubular Potassium Gradient (TTKG) is a renal potassium secretion index that estimates the gradient of potassium concentration between the tubular fluid and peritubular capillary blood in the cortical collecting duct.

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 equation corrects for water reabsorption in the collecting duct by using the urine-to-plasma osmolality ratio, providing a more accurate assessment of potassium handling in the distal nephron.

3. Importance of TTKG Calculation

Details: TTKG is clinically useful for differentiating between renal and extrarenal causes of hyperkalemia or hypokalemia, and for assessing the appropriateness of renal potassium handling in various clinical conditions.

4. Using the Calculator

Tips: Enter all values in their respective units. All values must be positive numbers. The result is unitless and represents the transtubular potassium gradient.

5. Frequently Asked Questions (FAQ)

Q1: What is the normal range for TTKG?
A: Normal TTKG ranges from 6-12 in healthy individuals on a normal diet. Values may vary depending on dietary potassium intake and other factors.

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

Q3: How is TTKG used in hypokalemia?
A: In hypokalemia, a TTKG >4 suggests renal potassium wasting, while a TTKG <2 suggests appropriate renal potassium conservation.

Q4: What are the limitations of TTKG?
A: TTKG is less reliable when urine osmolality is less than plasma osmolality, and it assumes minimal water reabsorption in the medullary collecting duct.

Q5: When should TTKG not be used?
A: TTKG should not be used when urine osmolality is less than serum osmolality, or in patients with significant renal impairment.