When is measuring the urine-blood PaCO2 gradient following an HCO3- load useful 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

Measuring the urine-blood PaCO2 gradient following an HCO3- load is useful in some patients with classic distal RTA to differentiate a permeability defect from other defects. This test is useful in patients with nephrocalcinosis in whom distal RTA is suspected but urine is acidified appropriately in the face of metabolic acidosis. Some of these patients have a rate-dependent defect in proton secretion, revealed by a low urine-blood PaCO2 gradient following HCO3- loading.


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