Q: What is the most important clinical relevance of TTKG (The trans-tubular potassium gradient)?

Answer: TTKG is calculated by following formula

TTKG = urine K+ X serum osmolality/serum K+ X urine osmolality

• A TTKG of greater than 8 indicates that aldosterone is present and that the collecting duct is responsive to it.
• A TTKG of less than 5 in the presence of hyperkalemia indicates aldosterone deficiency or resistance.