Cl- is the major extracellular negative ion in the body. Its main purpose is to maintain electrical neutrality, mostly as a counter-ion to sodium. It often accompanies sodium losses and excesses. It also affects acid-base balance. That is, as CO2 increases, bicarbonate moves from the intracellular space to the extracellular space. To maintain electrical neutrality, more chloride tends to enter cells.
Because of its relationship with other electrolytes, urinary chloride results can be used to help assess volume status, salt intake, causes of hypokalemia, and to aid in the diagnosis of renal tubular acidosis.
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