Direct fluorescent assays are best described by which statement?

Direct fluorescent assays are best described by which statement?

• A. The anti-immunoglobulin has the fluorescent tag.
• B. Antibody is attached to a solid phase.
• C. Microbial antigens can be rapidly identified by this method.
• D. The amount of color is in inverse proportion to the amount of antigen present.

Answer: (C)

Direct fluorescent assays work by using a fluorescently labeled antibody that binds directly to the target antigen in the specimen. This direct labeling lets you visualize the presence of the antigen right away under a fluorescence microscope, allowing rapid identification of pathogens. That makes the statement about microbial antigens being rapidly identified by this method the best description. If the fluorescent tag were on a secondary anti-immunoglobulin, you’d be describing an indirect fluorescent assay. Attaching the antibody to a solid phase is characteristic of solid-phase immunoassays like ELISA, not direct fluorescence. And the signal in a fluorescent assay isn’t an inverse color change with regard to antigen amount; instead, more antigen typically yields more fluorescence.

Direct fluorescent assays work by using a fluorescently labeled antibody that binds directly to the target antigen in the specimen. This direct labeling lets you visualize the presence of the antigen right away under a fluorescence microscope, allowing rapid identification of pathogens. That makes the statement about microbial antigens being rapidly identified by this method the best description.

If the fluorescent tag were on a secondary anti-immunoglobulin, you’d be describing an indirect fluorescent assay. Attaching the antibody to a solid phase is characteristic of solid-phase immunoassays like ELISA, not direct fluorescence. And the signal in a fluorescent assay isn’t an inverse color change with regard to antigen amount; instead, more antigen typically yields more fluorescence.