Chloride 21 FS is a colorimetric test to determine chloride in serum or lithium heparin plasma. Chloride is an important anion and essential in maintaining the anion-cation-balance in the body. Increased chloride values occur in dehydration, metabolic acidosis related with prolonged diarrhea and bicarbonate loss, renal insufficiencies and endocrinological disorders. Decreased values are observed in metabolic acidosis with increased production of organic acids, salt-losing nephritis and excessive sweating.