In lateral flow assays, what indicates a positive result in a competitive assay?

In a competitive assay format of lateral flow assays, a positive result is indicated by the presence of a visible line for the control only. This occurs because, in competitive assays, the target analyte present in the sample competes with the analyte that is coated onto the test line. If the target analyte is present in the sample, it binds to the detection antibodies before they can bind to the immobilized analyte on the test line. As a result, no line appears at the test position since the competitive analyte outcompetes the labeled detection antibodies.

Conversely, a visible control line will always appear to indicate that the assay is functioning properly, as it confirms that the sample has flowed through the device and that the reagents for the control line are active. Thus, the absence of a test line, combined with a visible control line, confirms a positive test result in such assay formats.

The other options do not represent the correct interpretation of a competitive assay result. A visible line for the test only would indicate a negative result, as it suggests that the target analyte was not present in sufficient quantities to compete with the immobilized analyte. No visible line signifies either a failure of the assay or that neither the control nor test conditions