we recently isolated Candida albicans from the CSF of an AIDS patient. The interesting fact was that using CrAg test it was positive but no Cryptococcus was isolated. The question is, can whats the rate for CrAg false positive results?
Sensitivity for CrAg is high but specificity is not 100% .
That means being sensitive alone may not be truely crypto.
Need further clearification let me know.
It depends on if you are using the LFA or the Latex aglutination. The rates should be around 1 and 4%, respectively. However, what has always been the dogma, is that a titer above 1:8 is never a false positive. The main exception is Trichosporon, which is the only fungus that cross reacts with the CrAg (J Clin Microbiol. 1985 May; 21(5): 681–685.)
The false positive results are usually related to infections by basidiomycetes (J Infect. 2015 May;70(5):499-503). Cross-reaction with Candida is quite surprising. Are you sure that the yeast you found in the CSF is Candida? Maybe co-infection with Crypto?
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