What is the role of lab testing in the evaluation of hyperchloremic acidosis?

Updated: Oct 18, 2018
  • Author: Sai-Ching Jim Yeung, MD, PhD, FACP; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

If the cause of a patient’s acidosis is not apparent from the history and physical examination findings, the next step is to determine whether hyperchloremic acidosis is present. Tests include the following:

  • Urinary ammonium excretion (urine AG; urine net charge) - This is inferred from the urine AG, also known as the urine net charge, when direct measurement of ammonium is not possible
  • Urinary pH - This tends to be increased in the presence of large amounts of ammonia in the urine
  • Acid-loading tests - The most common acid-loading test uses ammonium chloride (NH 4 Cl)
  • Urinary PCO 2 test - The urinary PCO 2 during alkaline diuresis reflects the rate of proton secretion in the distal tubule
  • Sodium sulfate test - In healthy individuals, administering a sodium salt of a nonreabsorbable anion in the presence of a sodium-avid state results in negative intratubular potential and thus in increased proton and potassium secretion; in patients with either secretory or voltage defects, the urine will not become maximally acidic
  • Furosemide test - Evidence suggests that furosemide enhances distal acidification by increasing distal sodium delivery; results should be interpreted in the same manner as for the sodium sulfate test

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