Transtubular K Gradient Calculation

TTKG Formula:

\[ TTKG = \frac{Urine\ K / Plasma\ K}{Urine\ Osm / Plasma\ Osm} \]

Urine K:

mmol/L

Plasma K:

mmol/L

Urine Osm:

mOsm/kg

Plasma Osm:

mOsm/kg

TTKG Result:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Transtubular K Gradient?

The Transtubular Potassium Gradient (TTKG) is a calculated value that assesses renal potassium handling. It 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 formula:

\[ TTKG = \frac{Urine\ K / Plasma\ K}{Urine\ Osm / Plasma\ Osm} \]

Where:

\( Urine\ K \) — Urine potassium concentration (mmol/L)
\( Plasma\ K \) — Plasma potassium concentration (mmol/L)
\( Urine\ Osm \) — Urine osmolality (mOsm/kg)
\( Plasma\ Osm \) — 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 potassium secretion in the cortical collecting duct.

3. Importance of TTKG Calculation

Details: TTKG is clinically useful for differentiating between renal and extrarenal causes of hyperkalemia or hypokalemia. It helps determine whether the kidneys are appropriately responding to potassium imbalances.

4. Using the Calculator

Tips: Enter all four required values in their respective units. Ensure urine osmolality is greater than plasma osmolality for accurate interpretation. All values must be positive numbers.

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. Values may vary depending on dietary potassium intake and other factors.

Q2: How is TTKG interpreted in hyperkalemia?
A: In hyperkalemia, TTKG > 10 suggests appropriate renal potassium excretion, while TTKG < 7 suggests impaired renal potassium excretion.

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

Q4: What are the limitations of TTKG?
A: TTKG is less reliable when urine osmolality is less than plasma osmolality, in the presence of osmotic diuresis, or with very low urine sodium.

Q5: When should TTKG not be used?
A: TTKG should not be used when urine osmolality is less than serum osmolality, as the calculation becomes invalid under these conditions.