Phenol red, a chemical, molecular formula C19H14O5S, is bright red to dark red crystal or fine crystalline powder. Phenol red is widely used as an acid-base indicator. It is commonly used for auxiliary diagnosis of renal function. Its monosodium salt is used by veterinarians for renal function tests, chromatographic analysis reagents, etc., as well as for the determination of total carbon dioxide in blood, indicator of disaccharide iron urea medium, etc. Acid base indicator, color change range pH: 6.8 (yellow) - 8.4 (red). The indicator for preparing disaccharide iron urea culture medium in the determination of total blood carbon dioxide and bacterial serum test. Its sodium salt is used to measure liver function. It is also used for biochemical research.