Evaluation of the semi-quantitative BIOSynex® CryptoPS test in serum and cerebrospinal fluid samples of patients with cryptococcosis diagnosed through the IMMY CrAg® lateral flow assay: a translational study

Abstract

The advent of lateral flow assays (LFAs) has significantly improved the diagnosis of cryptococcosis. While the widely used IMMY CrAg® LFA is qualitative, antigen titration requires multiple test strips, increasing cost and complexity. The BIOSynex® CryptoPS is a semi-quantitative LFA that categorizes antigen levels into two ranges, low (≤25 ng/ml in cerebrospinal fluid [CSF] or ≤50 ng/ml in serum) and high (≤2,500 ng/ml in both sample types). We evaluated the performance and prognostic relevance of this assay in 22 serum and 14 CSF samples from 23 patients with cryptococcosis. Seventeen patients had culture confirmed cryptococcosis, while six were diagnosed by isolated antigenemia using the IMMY CrAg® LFA. Three samples tested negative by BIOSynex® CryptoPS despite being positive by IMMY CrAg® LFA. Among culture positive patients, all showed high antigen levels in the BIOSynex® CryptoPS. Higher antigen levels were significantly associated with lower CD4 counts in people living with HIV/AIDS (P = 0.026) and more frequent cryptococcal meningitis (P = 0.040), though not fungemia (P = 0.144). Two deaths occurred in patients with high antigen levels. The BIOSynex® CryptoPS LFA demonstrated good agreement with IMMY CrAg® LFA and provided prognostic insights, highlighting its potential role in clinical risk stratification and early management of cryptococcosis.