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Definition of Sodium

  • 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.

Sodium: The major positive ion (cation) in the fluid surrounding cells in the body. The chemical notation for sodium is Na+. When sodium is combined with chloride, the resulting substance is a crystal called table salt. Excess dietary sodium is largely excreted in the urine, but too much salt in the diet tends to increase the blood pressure. Too much or too little sodium in the blood (called hypernatremia or hyponatremia respectively) can cause cells to malfunction, and extremes can be fatal. Normal blood sodium level is 135'145 milliEquivalents/liter (mEq/L) or 135'145 millimoles/liter (mmol/L) in international units.

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Reviewed on 12/27/2018

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