Transtubular potassium gradient

Serum, 1ml

Urine, 10ml

Evaluation

TTKG Interpretation of the data

8 - 9 Normal

Hyperkalemia
> 10 Normal aldosterone effect
< 5-7 Extrarenal cause of hyperkalemia, impaired potassium secretion in aldosterone deficiency/resistance

After administration of 0.05 mg 9-a-fludrocortisone (artificial mineralocorticoid)
Initial < 5-7, then > 10 Hypoaldosteronism probable
Initial < 5-7, no change K+-sparing diuretics (spironolactone, triamterene, amiloride), tubular aldosterone resistance (interst. nephritis, obstruction, pseudohypoaldosteronism type I, sickle cell disease), drugs (trimethoprim, pentamidine), increased distal K+ reabsorption (pseudohypoaldosteronism type II, obstruction).

Hypokalemia
< 2 extrarenal loss
> 2 renal loss


Literatur:
1) West ML et al. New clinical approach to evaluate disorders of potassium excretion. Miner Electrolyte Metab 1986; 12: 234+B18
2) Ethier JH et al. The transtubular potassium concentration in patients with hypokalemia and hyperkalemia. Am J Kidney Dis 1990; 15: 309
3) Rose BD, Post TW. Clinical physiology of acid-based and electrolyte disorders, 5th ed, McGraw-Hill, New York, 2001; pp. 900-901+B92