Saturday, May 28, 2011

Highest TTKG with hypokalemia

Patient with a lifelong history of hypokalemia. He came to me for a second opinion, his previous nephrologist had been nudging up his potassium dose on every visit and the patient was now on 70 mEq of KCl daily and was getting uncomfortable with endlessly increasing doses of potassium.

At the time I saw him these were his labs (he had decreased his potassium supplementation to 20 mEq/day):

  • Blood
    • sodium: 128
    • glucose: 90
    • potassium: 2.8
    • Creatinine: 0.9
    • BUN: 11
    • Magnesium: 1.8
    • Calculated osmolality: 265
  • Urine 
    • sodium: 135
    • potassium: >100
    • Osmolality: 637

Trans-tubular potassium gradient: 14.9. That's crazy high for a patient with hypokalemia, one should expect it to be less than 2 for hypokalemia of extra-renal origin, and only 7 or 8 for hypokalemia from hyperaldosteronism. Halperin et al. were not able to get the TTKG that high even when they took normokalemic patients and doped them with fludrocortisone and 50 mEq of oral potassium. 

And that 14.9 is assuming the urine potassium is 100, our lab doesn't do serial dilutions so who knows what the actual potassium is? 120? 140?

I'm still waiting for the renin and aldo but I smell some Bartter's
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