Evaluation of the Diagnostic Performance of a Semiquantitative Cryptococcal Antigen Point-of-Care Assay among HIV-Infected Persons with Cryptococcal Meningitis

Abstract

Introduction: A newly developed cryptococcal antigen (CrAg) semi-quantitative (SQ) lateral flow assay (LFA) provides a semi-quantitative result in a rapid, one-step test instead of performing serial dilutions to determine CrAg titer. Methodology: We prospectively compared the diagnostic performance of the CrAgSQ assay (IMMY) with the CrAg LFA (IMMY) on cerebrospinal fluid (CSF) samples collected from persons with HIV-associated meningitis. The CrAgSQ grades (1+ to 5+) were compared with CrAg LFA titers and quantitative CSF fungal cultures. Results: Among 87 participants screened for HIV-associated meningitis, 60 had cryptococcal meningitis (59 CrAg+ by LFA and 1 false negative due to prozone with CrAg LFA titer of 1:1,310,000 and culture positivity), and 27 had no cryptococcal meningitis by CrAg LFA or culture. The CrAgSQ on CSF had 100% (60/60) sensitivity and 100% specificity (27/27). CSF CrAg titers ranged from 1:5 to 1:42 million. CrAgSQ grade of 1+, 2+, 3+, 4+, and 5+ corresponded to median CrAg LFA titers of 1:<10, 1:60, 1:7,680, 1:81,920, and 1:1,474,000, respectively. CSF CrAgSQ 3+ or higher were always CSF culture positive. Mortality at 14 days for those with low CrAgSQ grade (1+ to 3+) was 5% (1/22) versus 21% (8/38) with high CrAgSQ grades (4+ to 5+) (P=.084). Conclusion: The CrAgSQ demonstrates excellent diagnostic performance, maintaining both the sensitivity and specificity of the CrAg LFA, and counters false negative prozone effects. The CrAgSQ assay reading is more complex but does provide useful clinical information about disease burden and probability of culture positivity in a single rapid diagnostic test.

Laboratory verification of new commercial lateral flow assays for Cryptococcal antigen (CrAg) detection against the predicate IMMY LFA in a reference laboratory in South Africa

“…These results confirm earlier reported verification results with this CrAg assay [43,44,46], where there was a good correlation with LFA titer results, where the grading from 1+ to 5+ showed correlation with titers [43,44,46]. This was further confirmed in a study on cerebrospinal fluid (CSF), where increasing IMMY SQ grades were associated with greater LFA titer and quantitative culture results/colony forming units (CFU/ml) [49]. The risk stratification offered by the IMMY SQ and Bio-Rad assays may be important from a clinical perspective to identify the severity of meningitis and the infiltration of the central nervous system (CNS) associated with elevated CrAg concentrations [43,44,46].…”

“…The risk stratification offered by the IMMY SQ and Bio-Rad assays may be important from a clinical perspective to identify the severity of meningitis and the infiltration of the central nervous system (CNS) associated with elevated CrAg concentrations [43, 44, 46]. Patients with a grade of ≥3 may have a higher risk of poor outcomes, as reported by Tadeo et al, 2021 [49].…”

Noninvasive Testing and Surrogate Markers in Invasive Fungal Diseases

“…Internationally, other non–Food and Drug Administration (FDA)–approved CrAg LFAs exist with substantially worse diagnostic performance [ 7–9 ]. Serum or plasma CrAg LFAs are >99.9% sensitive for detecting meningitis in HIV-infected persons with meningitis, although if central nervous system symptoms are present despite negative serum testing assessment of the CSF should be pursued [ 10 , 11 ]. False-negative tests are more common with CrAg latex agglutination and in HIV-negative persons, where ~20% may have a false-negative CrAg in serum with disseminated disease [ 3 , 12 ].…”

“…False-negative tests are more common with CrAg latex agglutination and in HIV-negative persons, where ~20% may have a false-negative CrAg in serum with disseminated disease [ 3 , 12 ]. False-negative CrAg LFAs are possible due to a prozone effect at CrAg titers >1:1 million by serial dilution; however, a new semiquantitative CrAg LFA has been developed that eliminates prozone [ 11 ]. The ability to provide a semiquantitative CrAg titer provides prognostic information, as high titers are correlated with high burden of disease and predict poor prognosis [ 13 , 14 ].…”

Comparative analysis of diagnostic methods for the detection of Cryptococcus neoformans meningitis

“…Currently, the laboratory diagnosis of Cryptococcus spp. is based on mycological, histopathological and serological tests [17][18][19][20][21][22][23][24][25][26]. The Brazilian Unified Health System (SUS) provides different methods for the diagnosis of CM.…”