1. What is the TTKG?

The Transtubular Potassium Gradient (TTKG) estimates the potassium concentration gradient between the lumen of the cortical collecting duct and the peritubular capillary. It helps differentiate between renal and extrarenal causes of hyperkalemia or hypokalemia.

2. How Does the Calculator Work?

The calculator uses the TTKG equation:

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 ratio corrects for water reabsorption in the medullary collecting duct, providing a more accurate assessment of potassium secretion in the cortical collecting duct.

3. Clinical Significance

Interpretation:

• Normal TTKG: 6-9
• Hypokalemia: TTKG < 2 suggests appropriate renal response (potassium conservation)
• Hyperkalemia: TTKG > 10 suggests appropriate renal response (potassium secretion)

4. Using the Calculator

Tips: Enter all values in appropriate units. Samples should be obtained simultaneously for accurate results. Urine osmolality should be greater than serum osmolality for valid interpretation.

5. Frequently Asked Questions (FAQ)

Q1: When is TTKG most useful?
A: Most helpful in evaluating hyperkalemia or hypokalemia when urine potassium is unexpectedly high or low.

Q2: What are limitations of TTKG?
A: Less reliable when urine osmolality < serum osmolality, with very low urine output, or with certain medications affecting potassium handling.

Q3: How should samples be collected?
A: Simultaneous blood and urine samples are ideal. Avoid contamination and process promptly.

Q4: Does TTKG apply to all patients?
A: Most validated in adults with normal renal function. Interpretation may differ in CKD or ESRD.

Q5: What factors can affect TTKG?
A: Aldosterone levels, diuretics, acid-base status, and urine flow rate can all influence TTKG.