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Definition of Anion gap

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Anion gap: A measurement of the interval between the sum of "routinely measured" cations minus the sum of the "routinely measured" anions in the blood. The anion gap = (Na+ + K+) - (Cl- + HCO3-) where Na- is sodium, K+ is potassium, Cl- is chloride, and HCO3- is bicarbonate.

The anion gap can be normal, high, or low. A high anion gap indicated metabolic acidosis, the increased acidity of the blood due to metabolic processes. A low anion gap is relatively rare but may occur from the presence of abnormal positively charged proteins, as in multiple myeloma.

Reviewed on 12/11/2018

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