A 32-year-old man with HIV (CD4 count 60 cells/µL) presents with 3 weeks of headache and low-grade fever. CSF shows WBC 25 cells/µL (lymphocytic), protein 70 mg/dL, glucose 30 mg/dL (blood glucose 110). Which test should be performed first to confirm the diagnosis?
- A CSF India ink preparation
- B Serum cryptococcal antigen
- C CSF cryptococcal antigen (CrAg) by lateral flow assay ✓
- D CSF mycobacterial culture
Correct answer: C. CSF cryptococcal antigen (CrAg) by lateral flow assay
Explanation
The chronic lymphocytic meningitis with low glucose in an advanced HIV patient strongly suggests cryptococcosis. The CSF CrAg lateral flow assay has sensitivity above 99% and outperforms India ink, which detects organisms in only about 50 to 60% of cases and is negative when yeast counts are low. Serum CrAg is highly sensitive but CSF testing confirms CNS disease directly. Mycobacterial culture takes weeks and would not explain the typical presentation.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.