Which of the following errors would result in positive results for all samples in an ELISA assay (including negative controls)?

A. Failure to perform the wash step after initial incubation with controls/samples,
B. Failure to perform the wash step after incubation with secondary antibody.
C. Failure to perform the wash step after incubation with primary antibody.

B. Failure to perform the wash step after incubation with secondary antibody, this because If the test sample did not contain antigen, primary antibody did not bind to the wells, so the secondary antibody did not have anything to bind to and was flushed out in the wash step, so the secondary antibody determines the antibody that appears.

The correct option is option B.

Explanation:

Failure to perform the wash step after incubation with secondary antibody.

This is true because the lack of the antigen causes the first antibody to pass through during the washing step. Thus this will lead to no substance for the second antibody to hold on and thus can lead to positive results in all the samples.