Evaluation of Point of Care Serum Cryptococcal Antigen by Lateral Flow Immunoassay for Diagnosis of Cryptococcosis and Cryptococcal Meningitis in HIV Positive Patients

Abstract

Background: Cryptococcal meningitis is the initial AIDS defining illness in 2% of patients with CD4 levels less than 100/μL and a leading cause of mortality in AIDS in the developing world. It is the most common opportunistic infection of the central nervous system in AIDS in various Indian studies. Detection of serum cryptococcal antigen (SCRAG) is the most widely used diagnostic method for cryptococcosis. Presence of cerebrospinal fluid cryptococcal antigen (CSF CRAG) is diagnostic of CM. CRAG can be determined by latex agglutination (LAT), ELISA and now, by lateral flow (LFA) immunoassay. LFA is a point of care test that rapidly detects CRAG. This study compares LAT and LFA for detection of serum CRAG and diagnosing CM. Method: 210 patients of HIV/AIDS were submitted to SCRAG LFA by dipstick. A sample was also sent to laboratory for SCRAG by LAT. CSF examination was done for those who were positive for SCRAG LFA and those who had symptoms suggestive of meningitis. SCRAG by LFA was compared with SCRAG by LAT, CSF CRAG by LAT and LFA, CSF cryptococcal culture and CSF India ink examination for Cryptococcus. Findings: Fifteen patients were found positive for SCRAG by LFA dipstick. All of them were also positive for SCRAG by LAT. Tweleve of them had CD4 count below 100 cells/mm3. CSF CRAG was positive in all 12 SCRAG positive who were submitted to CSF examination. Interpretation: We found that serum detection of cryptococcal antigen by LFA dipstick is as sensitive as CRAG detection in serum by LAT and CSF CRAG detection by LFA and LAT. It is thus a rapid test for diagnosing CM in HIV patients with low CD4 counts. Funding Statement: One of the authors (AC) was supported by the research grant from ICMR, Delhi vide grant no OMI/13/2014-ECD-I. Declaration of Interests: All authors declare no competing interests. Ethics Approval Statement: Ethical approval was taken from the institutional ethic committee for the study.