Electrolytes
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: William C. Shiel, Jr, MD, FACP, FACR
What are electrolytes?
Electrolytes are substances that become ions in solution
and acquire the capacity to conduct electricity. The balance of the electrolytes
in our bodies is essential for normal function of our cells and our organs.
Common electrolytes that are measured by doctors with blood testing include
sodium, potassium, chloride, and bicarbonate. The functions and normal range
values for these electrolytes are described below.
Sodium: Sodium is the major positive ion (cation) in fluid
outside of cells. The chemical notation for sodium is Na+. When combined with
chloride, the resulting substance is table salt. Excess sodium (such as from fast food
hamburger and fries) is excreted in the urine. Sodium regulates the total amount
of water in the body and the transmission of sodium into and out of individual
cells also plays a role in critical body functions. Many processes in the body,
especially in the brain, nervous system, and muscles, require electrical signals
for communication. The movement of sodium is critical in generation of these
electrical signals. Too much or too little sodium therefore can cause cells to
malfunction, and extremes (too much or too little) can be fatal. A Normal blood sodium level is 135 - 145 milliEquivalents/liter (mEq/L), or in international units, 135 - 145
millimoles/liter (mmol/L).
Potassium: Potassium is the
major positive ion (cation) found inside of cells. The chemical notation for
potassium is K+. The proper level of potassium is essential for normal cell
function. Among the many functions of potassium in the body are regulation of
the heartbeat and function of the muscles. A seriously abnormal increase of
potassium (hyperkalemia) or decrease
of potassium (hypokalemia) can profoundly affect the nervous system and
increases the chance of irregular heartbeats (arrhythmias), which, when extreme,
can be fatal.
The normal blood potassium level is 3.5 - 5.0 milliEquivalents/liter (mEq/L),
or in international units, 3.5 - 5.0 millimoles/liter (mmol/L).
Chloride: Chloride is the major anion (negatively charged ion) found
in the fluid outside of cells and in blood. An anion is the negatively charged
part of certain substances such as table salt (sodium chloride or NaCl) when
dissolved in liquid. Sea water has almost the same concentration of chloride ion
as human fluids. Chloride also plays a role in helping the body maintain a
normal balance of fluids.
The balance of chloride ion (Cl-) is closely regulated by the body.
Significant increases or decreases in chloride can have deleterious or even
fatal consequences:
The normal serum range for chloride is 98 - 108 mmol/L.
Bicarbonate: The bicarbonate ion acts as a buffer to maintain the
normal levels of acidity (pH) in blood and other fluids in the body. Bicarbonate
levels are measured to monitor the acidity of the blood and body fluids. The
acidity is affected by foods or medications that we ingest and the function of
the kidneys and lungs. The chemical notation for bicarbonate on most lab reports
is HCO3- or represented as the concentration of carbon dioxide (CO2). The normal
serum range for bicarbonate is 22-30 mmol/L.
Last Editorial Review: 1/4/2006
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