Acid phosphatase (Acid Phosphatase, ACP) is very widely distributed throughout a variety of tissues, mainly in the lysosomes of cells, so it is often used as a marker enzyme for lysosomes, and extra-lysosomal Acid Phosphatase exists in the endoplasmic reticulum and cytoplasm. Acid phosphatase varies in various animals, and the appropriate pH of acid phosphatase is 4.5-5.5. Tartrate-resistant acid phosphatase (TRAP), which exists in normal human alveolar macrophages and leukemic spleens, is in the cellular follicles and is not released into the bloodstream, and the vast majority of TRAP in blood originates from osteoclasts. The vast majority of TRAP in the blood originates from osteoclasts, so the functional status of osteoclasts can be understood by measuring TRAP in the blood.

Anti-tartaric acid acid phosphatase staining solution uses naphthol AS-BI as the substrate, which is hydrolyzed by acid phosphatase to release phosphoric acid and naphthol at acidic pH. Naphthol coupled with diazonium salts generates a colored product, which is localized in the cytoplasm, and is positively reacted if the intracellular ACP has anti-tartaric acid activity, and can be used in fresh blood smears, cellular smears, and frozen sections.