When the test lies: Fatal cryptococcosis and the prozone effect in advanced HIV infection.
Mylene Costa, Patrícia Rodrigues, Beatriz Araújo et al.
✦ AI-curated · Sources linked
Case in brief
A 37-year-old man with advanced HIV infection presented with altered mental status. Initial cryptococcal antigen (CrAg) tests on serum and cerebrospinal fluid (CSF) were negative. However, India ink staining revealed encapsulated yeasts, leading to positive CrAg results upon serial dilution. Cultures confirmed disseminated cryptococcosis. Despite treatment, the patient succumbed to neurological deterioration.
What made this case unusual
The case highlights the prozone effect, where high antigen levels lead to false-negative CrAg results, complicating diagnosis.
Diagnostic / clinical pearl
Clinicians should be aware of the prozone effect in cryptococcal antigen testing, especially in patients with advanced HIV, and consider retesting with serial dilutions when initial results are negative.
Why it matters
This case emphasizes the importance of integrating clinical findings with laboratory results to avoid misdiagnosis in life-threatening infections.