A 55-year-old renal transplant patient on tacrolimus develops subacute meningitis. CSF India ink preparation shows encapsulated yeast cells. CSF cryptococcal antigen (CrAg) lateral flow assay is strongly positive (titer 1:2048). The serum CrAg LFA is also positive. Which of the following about the CrAg LFA is CORRECT?
- A CrAg LFA has sensitivity >99% for cryptococcal meningitis and detects both C. neoformans and C. gattii ✓
- B A prozone effect causing false-negative result occurs at low antigen concentrations
- C CrAg LFA cannot be used on serum; it is valid only for CSF
- D A positive CrAg LFA requires confirmation with India ink before treatment can begin
Correct answer: A. CrAg LFA has sensitivity >99% for cryptococcal meningitis and detects both C. neoformans and C. gattii
Explanation
The cryptococcal antigen lateral flow assay (IMMY CrAg LFA) has sensitivity >99% and specificity >99% for cryptococcal meningitis and detects both C. neoformans var. neoformans/grubii and C. gattii, making it the preferred rapid diagnostic. It is validated for use on serum, plasma, urine, and CSF. Prozone false-negatives occur at very HIGH (not low) antigen concentrations in latex agglutination tests (less common with LFA). Treatment should not be delayed for India ink confirmation when LFA is positive.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.