In an immunodiffusion test to diagnose histoplasmosis, a patient's serum is placed in a well in an agar plate. In a positive test, a line forms as the serum diffuses from the well and meets material diffusing from a second well. What type of test is this?

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Quizplus · Accepted Answer

The immunodiffusion test described in the question is a precipitation reaction, where the interaction between antigen and antibody results in the formation of insoluble complexes which appear as a line of precipitation. ELISA, agglutination reaction, and complement-fixation tests are all different types of immunoassays, but they do not involve the precipitation of antigen-antibody complexes. A direct test typically refers to the visualization of a pathogen using specific antibodies without the use of a secondary antibody or detection system, which is not the case in the immunodiffusion test described.

In an Immunodiffusion Test to Diagnose Histoplasmosis, a Patient's Serum