What effect does ketonuria have on the urinary anion gap (AG) in 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 presence of ketonuria makes this test unreliable because the negatively charged ketones are unmeasured and urine AG will be positive or zero despite the fact that renal acidification and NH4+ levels are increased. Moreover, severe volume depletion from extrarenal NaHCO3 loss causes avid proximal Na+ reabsorption, with little Na+ reaching the lumen of the collecting duct to be reabsorbed in exchange for H+. Limiting H+ excretion reduces NH4+ excretion and may make the urine AG become positive.


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