Phthalein dyes are a class of dyes mainly used as pH indicators, due to their ability to change colors depending on pH.[1] They are formed by the reaction of phthalic anhydride with various phenols. They are a subclass of triarylmethane dyes.
Bromsulfthalein (also known as bromsulphthalein, bromosulfophthalein, and BSP) is a phthalein dye used in liver function tests. Determining the rate of removal of the dye from the bloodstream gives a measure of liver function.
Binding of sulfobromophthalein (BSP) sodium and indocyanine green (ICG) by plasma alpha-1 lipoproteins 1).