Paper II
Question
Lab diagnosis of cryptococcus
Answer
Laboratory diagnosis of Cryptococcus infection (cryptococcosis):
- India ink preparation of CSF — demonstrates the characteristic encapsulated yeast (a clear halo around the cell against the dark background) — a rapid, classic bedside test, though only moderately sensitive.
- Cryptococcal antigen (CrAg) test — latex agglutination or lateral flow immunoassay on CSF or serum, detecting capsular polysaccharide antigen; highly sensitive/specific, now the preferred rapid diagnostic test.
- Culture — on Sabouraud dextrose agar, confirms diagnosis and allows species identification/susceptibility testing.
- CSF examination — typically lymphocytic pleocytosis with often markedly raised opening pressure (an important prognostic and management factor, treated with therapeutic CSF drainage).
- Histopathology — mucicarmine stain highlights the polysaccharide capsule in tissue biopsy.