Chloride is the major negatively charged electrolyte (anion) in blood and extracellular fluid. It works closely with sodium to maintain fluid balance, blood pressure, and electrical neutrality across cell membranes. Chloride also forms part of hydrochloric acid in the stomach, essential for protein digestion and pathogen defence.

Chloride levels rise with dehydration, hypernatraemia, renal tubular acidosis, and excessive saline administration. Low chloride (hypochloraemia) is seen with prolonged vomiting, severe sweating, diuretic use, and adrenal insufficiency. Chloride is measured as part of the standard electrolyte panel and is used alongside sodium, potassium, and bicarbonate to calculate the anion gap and assess acid-base balance.