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

TTKG Result:

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1. What is Transtubular Potassium Gradient?

The Transtubular Potassium Gradient (TTKG) is a calculated index used to assess renal potassium handling and diagnose the etiology of hyperkalemia. It estimates the potassium concentration gradient between the tubular fluid and peritubular capillaries 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 TTKG corrects for the effect of water reabsorption in the medullary collecting duct, providing a more accurate assessment of cortical collecting duct potassium secretion.

3. Importance of TTKG Calculation

Details: TTKG is particularly useful in differentiating renal from non-renal causes of hyperkalemia. A low TTKG (<5-7) in the setting of hyperkalemia suggests inadequate renal potassium excretion, while a high TTKG (>7-10) suggests appropriate renal response.

4. Using the Calculator

Tips: Enter all four required values in appropriate units. Ensure urine and plasma samples are collected simultaneously for accurate results. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the normal range for TTKG?
A: In normokalemic individuals, TTKG typically ranges from 6 to 12. Values may vary depending on dietary potassium intake and other factors.

Q2: When is TTKG most useful clinically?
A: TTKG is most valuable in evaluating hyperkalemia to determine if the kidneys are responding appropriately by increasing potassium excretion.

Q3: What are the limitations of TTKG?
A: TTKG may be unreliable when urine osmolality is less than plasma osmolality or in the presence of significant water diuresis. It also assumes minimal potassium reabsorption in the medullary collecting duct.

Q4: How should samples be collected?
A: Simultaneous urine and plasma samples should be obtained. The patient should not be on potassium supplements or medications that significantly affect potassium handling at the time of testing.

Q5: What TTKG values suggest renal causes of hyperkalemia?
A: A TTKG <5-7 in the presence of hyperkalemia suggests impaired renal potassium excretion, potentially due to hypoaldosteronism, renal tubular acidosis, or medication effects.