False-Negative Cryptococcal Antigen Test

THE LATEX slide agglutination (LA) test for cryptococcal antigen in the CSF is more sensitive than the India ink preparation for diagnosing cryptococcal meningitis1,2and is the most widely used immunologic test for this disease. We describe here a previously unreported cause of negative LA test results in CSF in a patient with cryptococcal meningitis. Report of a Case A 64-year-old man with rheumatoid arthritis receiving 15 mg of prednisone daily had a fever, headache, confusion, and vertigo of three weeks' duration. Initial physical examination demonstrated delirium and meningismus. Lumbar puncture showed an opening pressure of 360 mm of CSF; glucose level, 49 mL/dL; protein level, 105 mg/dL; and WBC count, 40/cu mm. India ink preparation showed many budding yeast with thick capsules. The LA test results for cryptococcal antigen in CSF were initially reported as negative. The CSF cultures subsequently grew tan colonies of budding yeast that were