What is being tested?
Chloride is an electrolyte, a negatively charged molecule that works with other electrolytes, such as potassium, sodium, and total carbon dioxide (CO2), to help regulate the amount of fluid in the body and maintain the acid-base balance. Chloride is present in all body fluids but is found in the highest concentration in the blood and in the fluid outside of the body’s cells. Most of the time, chloride concentrations mirror those of sodium, increasing and decreasing for the same reasons and in direct relationship to sodium. When there is an acid-base imbalance, however, blood chloride levels can change independently of sodium levels as chloride acts as a buffer. It helps to maintain electrical neutrality at the cellular level by moving into or out of the cells as needed.

Chloride is taken into the body through food and table salt, which is made up of sodium and chloride molecules. Most of the chloride is absorbed by the gastrointestinal tract, and the excess is excreted in urine. The normal blood level remains steady, with a slight drop after meals (because the stomach produces acid after eating, using chloride from blood).

How is the sample collected for testing?
A blood sample is taken by needle from the arm. Chloride can also be measured in a urine sample.