A 28-year-old woman with HIV infection (CD4 count 280 cells/μL) on ART for 18 months presents with fever, headache, and neck stiffness. CSF analysis shows elevated protein (120 mg/dL), low glucose (35 mg/dL), and negative bacterial culture. Which investigation is most appropriate to confirm the suspected diagnosis of HIV-associated cryptococcal meningitis?

## Diagnosis of Cryptococcal Meningitis in HIV **Key Point:** CSF cryptococcal antigen (CrAg) test and India ink stain are the gold standard investigations for confirming cryptococcal meningitis in HIV patients with CD4 < 100 cells/μL. ### Clinical Presentation & Context This patient presents with classic meningitis signs (fever, headache, neck stiffness) and CSF findings typical of cryptococcal meningitis: - **Elevated protein** (usually 50–200 mg/dL) - **Low glucose** (typically 20–40 mg/dL) - **Negative bacterial culture** (rules out bacterial meningitis) - **CD4 < 100 cells/μL** (major risk factor for cryptococcal disease) ### Diagnostic Methods | Investigation | Sensitivity | Specificity | Timing | Notes | |---|---|---|---|---| | **CSF CrAg test** | 95–100% | 99% | Rapid (hours) | **Gold standard** — highly sensitive and specific | | **India ink stain** | 50–80% | 99% | Rapid (minutes) | Operator-dependent; lower sensitivity but rapid | | **CSF culture** | 70–90% | 100% | 1–2 weeks | Gold standard for species ID but slow | | Blood CrAg | 90–95% | 99% | Rapid | Positive in ~95% of cryptococcal meningitis; can be done first | | MRI brain | — | — | — | Shows hydrocephalus, mass effect; not diagnostic | **High-Yield:** **CSF CrAg is the single most useful test** because it is rapid, highly sensitive (95–100%), and highly specific (99%). It should be performed in all HIV patients with CD4 < 100 and meningitis symptoms [cite:Harrison 21e Ch 197]. ### Mnemonic for Cryptococcal Meningitis Diagnosis **"CrAg INK"** - **Cr**yptococcal **Ag**ent → CSF CrAg test (most sensitive) - **IN**dia **K**ink stain (rapid but less sensitive) ### Clinical Pearl In resource-limited settings (including India), **serum/blood CrAg screening** is increasingly recommended as a first step in CD4 < 100 patients, even without meningitis symptoms, because: 1. It is positive in ~95% of cryptococcal meningitis cases 2. Early detection allows preemptive fluconazole therapy 3. Reduces mortality when combined with ART optimization