The halides column in the periodic table consist of four elements: Fluorine, Chlorine, Bromine and Iodine. Of these Iodine and Chlorine are essential. Fluorine is used to fortify teeth enamel with an associated controversy. Bromine, previously thought inessential, has shown to be preferably utilized by certain immune cells. The most prevalent halide, chlorine, exists as salt and also as toxic forms such as perchlorates (from jet fuel, found in mother milk) and chloramines in drinking water.

The halide test measures levels of iodide, fluoride and bromide under baseline and challenged conditions.