Which statement describes a negative IDEXX heartworm result?

Which statement describes a negative IDEXX heartworm result?

• A. All antigen indicators show color
• B. Only positive control spot develops
• C. No controls show color
• D. Only negative control spot develops

Answer: (B)

A negative IDEXX heartworm result is defined by a valid run with no heartworm antigen detected. In this scenario, the positive control must show color to confirm the assay worked, while the antigen indicator spots remain colorless because there is no antigen in the sample. The negative control should also remain colorless, indicating no contamination or nonspecific color. So the description that only the positive control spot develops matches a proper negative result: the test ran correctly (positive control colored) but no antigen was present (test spots colorless) and there’s no color in the negative control. Other patterns would indicate a positive result or an invalid test run.

A negative IDEXX heartworm result is defined by a valid run with no heartworm antigen detected. In this scenario, the positive control must show color to confirm the assay worked, while the antigen indicator spots remain colorless because there is no antigen in the sample. The negative control should also remain colorless, indicating no contamination or nonspecific color. So the description that only the positive control spot develops matches a proper negative result: the test ran correctly (positive control colored) but no antigen was present (test spots colorless) and there’s no color in the negative control. Other patterns would indicate a positive result or an invalid test run.