Antigen test strips are not a substitute for pregnancy tests, they are completely different types of test strips. Antigens are used to detect symptoms of infection by taking a blood sample and testing the level of antigens in the blood sample. Antigen test strips are usually used to detect susceptibility to infectious diseases, and can help to initially screen people for possible infections, thus leading to further clinical diagnosis and testing. Pregnancy test strips, on the other hand, are generally used for women who are preparing for pregnancy and require a urine sample to be collected and placed on the surface of the test strip to determine whether or not the pregnancy has been successful through the results displayed on the test strip. The test is mainly used to determine pregnancy by detecting HCG levels in urine, and if further diagnosis is desired, hormone levels and ultrasound are required. Both test strips have different principles of use and scope of application, and therefore cannot be used in place of each other.