Causes of a False-Negative Immunoassay for Cryptococcal Antigen

Conditions associated with a cryptococcal infection and negative immunoassay for antigen:

(1) postzone (prozone, hook) effect

(2) cryptococcal species other than Cryptococcus neoformans

(3) capsular-deficient variants (small colony variant)

(4) laboratory error

where:

• The presence of a species other than C. neoformans is not necessarily a false negative since the species does not have the capsular antigen. In a sense this is a true negative, but a clinician would view it as a false negative.