Transtubular Potassium Gradient (TTKG) Calculator

1. What is a Transtubular Potassium Gradient (TTKG) Calculator?

Definition: The Transtubular Potassium Gradient (TTKG) Calculator estimates the potassium gradient across the cortical collecting duct, reflecting aldosterone activity and potassium secretion in the kidneys.

Purpose: It helps clinicians evaluate the cause of abnormal potassium levels (hyperkalemia or hypokalemia) by assessing renal potassium handling.

2. How Does the Calculator Work?

The calculator uses the following formula:

TTKG:
\( \text{TTKG} = \frac{\text{Urine Potassium} \times \text{Serum Osmolality}}{\text{Serum Potassium} \times \text{Urine Osmolality}} \)

Steps:

Input Serum Potassium (mmol/L), Urine Potassium (mmol/L), Serum Osmolality (mOsm/kg H₂O), and Urine Osmolality (mOsm/kg H₂O).
Validate inputs (all values must be greater than zero).
Calculate TTKG using the formula.
Display the result, rounded to 2 decimal places.

3. Importance of TTKG Calculations

Calculating TTKG is important for:

Diagnosing Potassium Disorders: A TTKG < 3 in hypokalemia suggests non-renal potassium loss, while a TTKG > 7 in hyperkalemia indicates renal potassium retention issues.
Assessing Aldosterone Activity: TTKG reflects aldosterone-driven potassium secretion; low values may indicate hypoaldosteronism, while high values suggest hyperaldosteronism.
Guiding Treatment: Helps determine the underlying cause of potassium imbalances to guide appropriate therapy, such as aldosterone replacement or potassium supplementation.

4. Using the Calculator

Examples:

Example 1: Serum Potassium: 4 mmol/L, Urine Potassium: 40 mmol/L, Serum Osmolality: 280 mOsm/kg H₂O, Urine Osmolality: 560 mOsm/kg H₂O
- TTKG: \( \frac{40 \times 280}{4 \times 560} = \frac{11200}{2240} = 5.00 \)
Example 2: Serum Potassium: 5 mmol/L, Urine Potassium: 20 mmol/L, Serum Osmolality: 300 mOsm/kg H₂O, Urine Osmolality: 600 mOsm/kg H₂O
- TTKG: \( \frac{20 \times 300}{5 \times 600} = \frac{6000}{3000} = 2.00 \)

5. Frequently Asked Questions (FAQ)

Q: What does a low TTKG indicate?
A: A TTKG < 3 in hypokalemia suggests non-renal potassium loss (e.g., gastrointestinal loss), while in hyperkalemia, it may indicate reduced aldosterone activity.

Q: What does a high TTKG indicate?
A: A TTKG > 7 in hyperkalemia suggests increased renal potassium secretion, possibly due to hyperaldosteronism or tubular dysfunction.

Q: When should TTKG not be used?
A: TTKG is less reliable if urine osmolality is not greater than serum osmolality or in acute settings with rapidly changing potassium levels—consult a healthcare provider.