A patient’s red blood cells are tested with anti‑A and anti‑B sera. Agglutination occurs with anti‑B but not with anti‑A. What is the patient's ABO blood type?

At the molecular level, which property of antibodies most directly enables the formation of visible antigen–antibody lattices in agglutination and precipitation assays?

A technician runs an indirect latex agglutination assay and obtains no visible clumping in a patient sample, while the positive control clumps normally. Which explanation is most consistent with a false‑negative caused by the prozone phenomenon?

In a double immunodiffusion (Ouchterlony) test, what is the ‘zone of equivalence’?

You are preparing a 4‑well control matrix for a diagnostic indirect agglutination assay: Well 1 = patient sample + test beads; Well 2 = patient sample + negative control beads; Well 3 = known positive antigen + test beads; Well 4 = buffer + test beads. Which interpretation of results (agglutination present/absent in each well) validates that a positive result in Well 1 is a true positive?