Which CSF analysis findings are characteristic of CNS cryptococcosis in HIV infection?

Updated: Jan 08, 2020
  • Author: Felicia J Gliksman, DO, MPH; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Answer

Measurement of opening pressure is an important aspect of lumbar puncture. Opening pressure is elevated to greater than 25cm H20 in approximately 60-80% of patients. [8, 9]  CSF analysis may yield normal (ie, reference) results in 25% of patients and may be minimally abnormal in as many as 50%; therefore, identifying the organism via India Ink and serology is crucial.

CSF fluid appearance can be clear or turbid. Protein levels exceed 45 mg/dL in one third to two thirds of cases, ranging from normal to 300 mg/100 dL. The glucose level is usually normal and is less than 60% of the serum level in only 17-65%.

Mononuclear pleocytosis (>20 cells/μL) occurs in 13-31% of cases. Numbers vary between reports, but in one study, 55% of patients had fewer than 10 mononuclear cells/μL.

Close to 100% of CSF culture results are positive for Cryptococcus neoformans, whereas 55% of blood culture results are positive. India ink stain is positive in 60-80% of infected patients but many labs in the United States no longer perform this test. 

Testing for CSF and serum cryptococcal antigen (CrAg) may be diagnostic with a sensitivity of 94.1% and 93.6%, respectively; a negative test should not be used as a rationale to discontinue treatment. CrAg may be present weeks to months before symptom onset [10] and a positive serum CrAg warrants a lumbar puncture to assess for meningeal infection. Antigen is detected via latex agglutination, enzyme immunoassays, and lateral flow assay.  Testing for CrAg in the serum is a useful initial screening tool in HIV-infected patients. [11]  A positive titer is sufficient to initiate therapy while cultures are pending in the appropriate clinical setting.


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