Unexpected Variability in Laboratory and Clinical Assays Used to Quantify Cryptococcus neoformans Polysaccharide

Area of Science:

• Medical Microbiology
• Immunodiagnostics
• Infectious Diseases

Background:

• Cryptococcal capsular polysaccharide (PS) antigen detection is vital for diagnosing cryptococcosis.
• Existing diagnostic assays exhibit variable sensitivity, impacting clinical utility.

Purpose of the Study:

• To compare the sensitivity of laboratory and clinical assays for cryptococcal PS antigen detection.
• To investigate the impact of Cryptococcus strain variation on assay performance.
• To identify reasons for false-negative results in cryptococcal antigen testing.

Main Methods:

• Evaluated four laboratory assays and two clinical assays (lateral flow assay (LFA) and cryptococcal latex agglutination assay (CLAA)) using PS from four Cryptococcus strains.
• Analyzed false-negative isolates from LFA to understand unrecognized PS motif expression.

Main Results:

• Laboratory assays showed consistent inter-strain sensitivity, while clinical assays exhibited significant variation linked to antigenic differences.
• False-negative LFA results were associated with cryptococcal PS motif expression not recognized by assay antibodies.
• Strain variation in PS structure directly impacts the sensitivity of quantification tests.

Conclusions:

• Antigen-antibody specificity is critical for accurate cryptococcal antigen testing in bodily fluids.
• Enhancing antibody specificity in clinical assays can potentially decrease false-negative results.
• Cryptococcal strain variability necessitates careful assay selection and development for reliable diagnosis.