India ink preparation

Principle

Ink particles cannot enter the polysaccharide capsule of Cryptococcus, so the capsule shows as a clear halo around the yeast on a dark background.

Procedure

• Centrifuge CSF and mix a drop of sediment with a small drop of India ink (or nigrosin) on a slide.
• Cover with a coverslip and examine with low power, then high power.

Results

• Positive: round budding yeasts with a wide clear halo

Notes

• Sensitivity is only about 50–80%; cryptococcal antigen (lateral flow or latex) is preferred.
• Lymphocytes and air bubbles can mimic yeasts; look for budding and a refractile cell wall.