TTKG Calculator
Calculate the transtubular potassium gradient (TTKG) to evaluate renal potassium handling. Differentiate renal from non-renal causes of hyperkalemia and hypokalemia with instant interpretation, breakdowns, and charts.
Note: Urine osmolality should be ≥300 mOsm/kg and urine sodium ≥25 mmol/L for accurate TTKG calculation.
About This Calculator
The TTKG (Transtubular Potassium Gradient) Calculator is a clinical tool used by nephrologists, internists, and healthcare professionals to evaluate renal potassium handling. It helps determine whether abnormalities in serum potassium levels are due to appropriate or inappropriate renal responses, aiding in the diagnosis of conditions such as hypoaldosteronism, pseudohypoaldosteronism, and type IV renal tubular acidosis.
The TTKG is calculated using the formula: TTKG = (Urine K / Serum K) / (Urine Osmolality / Serum Osmolality). This formula normalizes the potassium concentration gradient for water reabsorption in the distal nephron by incorporating both urine and serum osmolality. A urine osmolality of at least 300 mOsm/kg and urine sodium concentration of at least 25 mmol/L are required for accurate interpretation.
TTKG Interpretation Guide: In hypokalemia (serum K <3.5 mmol/L), TTKG <3 is appropriate (kidneys conserving K), while TTKG >3 suggests renal K wasting. In normokalemia (3.5-5.0 mmol/L), TTKG 8-9 is normal — values <8 or >9 warrant investigation. In hyperkalemia (>5.0 mmol/L), TTKG >7 indicates appropriate K excretion (optimally >10), while TTKG <7 points to type IV renal tubular acidosis or aldosterone deficiency.
Regional Notes: The TTKG formula and interpretation are universal and apply equally in India, the US, the UK, and all other regions. Reference ranges for serum potassium (3.5-5.0 mmol/L), serum osmolality (275-295 mOsm/kg), and urine osmolality (300-900 mOsm/kg) are consistent across clinical laboratories worldwide. Always interpret TTKG results in conjunction with other clinical parameters including blood pressure, volume status, renin and aldosterone levels, and medication history.
Frequently Asked Questions
What is TTKG in nephrology?
TTKG (Transtubular Potassium Gradient) is a clinical parameter used to evaluate renal potassium handling. It assesses whether the kidneys are appropriately responding to abnormal serum potassium levels by comparing potassium concentrations in urine and serum, normalized for water reabsorption using urine and serum osmolality.
How is TTKG calculated?
TTKG is calculated using the formula: TTKG = (Urine K / Serum K) / (Urine Osmolality / Serum Osmolality). This is equivalent to (Urine K × Serum Osmolality) / (Serum K × Urine Osmolality). The result should be interpreted in the context of the patient's serum potassium level.
What is a normal TTKG value?
Normal TTKG interpretation depends on serum potassium. In normokalemia (serum K 3.5-5.0 mmol/L), TTKG 8-9 is normal. In hyperkalemia (>5.0 mmol/L), TTKG >7 indicates appropriate renal response (optimally >10). In hypokalemia (<3.5 mmol/L), TTKG <3 is normal. Abnormal values suggest renal causes of potassium imbalance.
What conditions affect TTKG values?
Abnormal TTKG values can indicate hypoaldosteronism, pseudohypoaldosteronism, type IV renal tubular acidosis, diuretic use, or renal potassium wasting. In hyperkalemia with TTKG <7, consider aldosterone deficiency or resistance. In hypokalemia with TTKG >3, suspect renal potassium losses.
When should TTKG not be used?
TTKG is only reliable when urine osmolality is ≥300 mOsm/kg (indicating adequate ADH effect) and urine sodium concentration is ≥25 mmol/L. If these conditions are not met, the TTKG calculation may not accurately reflect distal nephron potassium handling and alternative assessments like 24-hour urine potassium should be considered.
Is the TTKG calculator free?
Yes, this TTKG calculator is completely free to use with no registration required. It provides instant results with clinical interpretation, breakdowns, and charts for both hyperkalemia and hypokalemia assessment.
Can I share my TTKG calculation results?
Yes, the URL automatically saves your input values so you can share the calculation link with colleagues or save it for later reference. Simply copy the URL after calculating.
What other renal calculators are available?
This site offers several related renal calculators including FENa (Fractional Excretion of Sodium), creatinine clearance (CrCl), BUN/creatinine ratio, anion gap, and urine output calculators. These tools together provide comprehensive renal function assessment.