Which assay is used to detect cryptococcal polysaccharide capsule antigen in patient serum or CSF?

Which assay is used to detect cryptococcal polysaccharide capsule antigen in patient serum or CSF?

• A. Latex agglutination
• B. India ink
• C. Complement fixation
• D. Hemagglutination

Answer: (A)

Detecting cryptococcal polysaccharide capsule antigen in serum or CSF is best done with latex agglutination. In this test, latex beads coated with antibodies against the cryptococcal capsule antigen cross-link if the antigen is present, producing visible clumping. This method is highly sensitive and works well for both serum and CSF, making it the go-to assay for diagnosing cryptococcal meningitis and for monitoring antigen levels. India ink visualization shows encapsulated yeast directly in CSF but is less sensitive, especially at low organism burden, and doesn’t measure soluble antigen levels. Complement fixation and hemagglutination are older techniques and are not as effective for detecting cryptococcal capsule antigen.

Detecting cryptococcal polysaccharide capsule antigen in serum or CSF is best done with latex agglutination. In this test, latex beads coated with antibodies against the cryptococcal capsule antigen cross-link if the antigen is present, producing visible clumping. This method is highly sensitive and works well for both serum and CSF, making it the go-to assay for diagnosing cryptococcal meningitis and for monitoring antigen levels. India ink visualization shows encapsulated yeast directly in CSF but is less sensitive, especially at low organism burden, and doesn’t measure soluble antigen levels. Complement fixation and hemagglutination are older techniques and are not as effective for detecting cryptococcal capsule antigen.