A protein that recognizes the drug site of an antibody-drug conjugate. The antibody-drug conjugate bonds a drug and an antibody represented by the following formula through a linker； and a quantitative method that uses the protein to quantify A method of confirming the concentration of the antibody-drug conjugate in plasma in a mammal administered the antibody-drug conjugate described above； and a method of confirming that the protein is used to confirm the binding of the antibody-drug conjugate administered above The method of tissue distribution of the antibody-drug conjugate in mammals.一種辨識抗體-藥物結合物的藥物部位之蛋白質，該抗體-藥物結合物係透過連接子而鍵結下式所示之藥物與抗體；及一種定量之方法，其係使用該蛋白質來定量在經投予上述之抗體-藥物結合物的哺乳動物中，該抗體-藥物結合物的血漿中濃度的方法；以及一種確認之方法，其係使用該蛋白質來確認在經投予上述之抗體-藥物結合物的哺乳動物中，該抗體-藥物結合物的組織分布的方法。
