What the role of the NH4 Cl loading test in the workup of metabolic acidosis?

Updated: Oct 10, 2018
  • Author: Christie P Thomas, MBBS, FRCP, FASN, FAHA; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

The NH4 Cl loading test is useful in patients with nephrocalcinosis and/or nephrolithiasis, who may have an incomplete form of distal RTA. These patients may not have a pH less than 7.35 or a drop in serum HCO3-; metabolic acidosis can be induced by administration of NH4 Cl (0.1 g/kg for 3 d). Under these circumstances of induced acidemia, a urine pH greater than 5.3 indicates distal RTA.

A recently described alternative to the NH4 Cl loading test involves the simultaneous oral administration of furosemide to increase distal Na+ delivery and fludrocortisone to increase collecting duct Na+ absorption and proton secretion. [9] Under these circumstances, a urine pH greater than 5.3 indicates distal RTA.


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