Final answer:
Serological tests for IgM antibodies are used to diagnose toxoplasmosis by detecting these antibodies in the patient's serum, using agglutination assays.
Step-by-step explanation:
The question relates to the diagnosis of toxoplasmosis, a disease caused by the pathogen Toxoplasma gondii. To diagnose this illness, serological tests are used to detect the presence of specific antibodies in the patient's serum. The serological test seeks the presence of IgM antibodies, which indicate a recent infection. These antibodies have a structure that allows for maximum cross-linking during an agglutination test, causing the beads to agglutinate indirectly and, thus, signaling a positive result. Typically, in cases of toxoplasmosis, a positive agglutination test will occur if the patient's serum contains IgM antibodies against Toxoplasma gondii antigens.