Questions: All of the following are correct about the indirect ELISA, except Multiple Choice it can detect antibodies in a serum sample. it is the common screening test for antibodies to Helicobacter. color development indicates that antibody was not present in the patient's serum. it is the common screening test for antibodies to Hepatitis A. a known antigen is adsorbed to the surface of a well.

The answer is: color development indicates that antibody was not present in the patient's serum.

Explanation for each option:

1. It can detect antibodies in a serum sample.

   • This is correct. Indirect ELISA is designed to detect the presence of specific antibodies in a serum sample by using an antigen that the antibody would bind to.

2. It is the common screening test for antibodies to Helicobacter.

   • This is correct. Indirect ELISA is commonly used to screen for antibodies against various pathogens, including Helicobacter pylori.

3. Color development indicates that antibody was not present in the patient's serum.

   • This is incorrect. In an indirect ELISA, color development indicates that the antibody was present in the patient's serum. The color change occurs because the enzyme-linked secondary antibody binds to the primary antibody, which is bound to the antigen.

4. It is the common screening test for antibodies to Hepatitis A.

   • This is correct. Indirect ELISA is also used to screen for antibodies against Hepatitis A virus.

5. A known antigen is adsorbed to the surface of a well.

   • This is correct. In an indirect ELISA, a known antigen is adsorbed to the surface of the well to capture the specific antibodies from the serum sample.

Summary: The incorrect statement about the indirect ELISA is that color development indicates that antibody was not present in the patient's serum. In reality, color development indicates the presence of the antibody.