Which serological test detects the polysaccharide capsule antigen in serum and CSF of patients with suspected Cryptococcus neoformans infection?

Which serological test detects the polysaccharide capsule antigen in serum and CSF of patients with suspected Cryptococcus neoformans infection?

• A. Complement fixation (CF)
• B. India ink test
• C. Latex agglutination (LA)
• D. Hemagglutination test

Answer: (C)

The test hinges on directly detecting the Cryptococcus capsule polysaccharide antigen in body fluids. Latex agglutination uses latex beads coated with antibodies against that capsule antigen; when the antigen is present in serum or CSF, it binds multiple beads and cross-links them, producing visible clumping. This makes the assay rapid and sensitive for cryptococcal meningitis, since the capsule antigen is shed into those fluids and can be detected even when organisms are few. By contrast, India ink is a direct visualization method to see the organism itself in CSF, not a serologic antigen test. Complement fixation detects antibodies or immune complexes rather than the capsule antigen itself, and hemagglutination isn’t used for detecting cryptococcal capsule antigen. So the latex agglutination approach best fits the goal of detecting the polysaccharide capsule antigen in serum and CSF.

The test hinges on directly detecting the Cryptococcus capsule polysaccharide antigen in body fluids. Latex agglutination uses latex beads coated with antibodies against that capsule antigen; when the antigen is present in serum or CSF, it binds multiple beads and cross-links them, producing visible clumping. This makes the assay rapid and sensitive for cryptococcal meningitis, since the capsule antigen is shed into those fluids and can be detected even when organisms are few. By contrast, India ink is a direct visualization method to see the organism itself in CSF, not a serologic antigen test. Complement fixation detects antibodies or immune complexes rather than the capsule antigen itself, and hemagglutination isn’t used for detecting cryptococcal capsule antigen. So the latex agglutination approach best fits the goal of detecting the polysaccharide capsule antigen in serum and CSF.