# Evaluation of a Multiplex Electrochemiluminescence Assay for Detection of Anti-Pneumococcal Antibodies in the Diagnosis of Selective Polysaccharide Antibody Deficiency

## TL;DR

This study evaluates a new rapid test for detecting antibodies against pneumococcal bacteria to diagnose a specific immune deficiency.

## Contribution

The study introduces and validates a multiplex electrochemiluminescence assay as a faster alternative to traditional methods for SPAD diagnosis.

## Key findings

- The ECL-plex assay showed strong correlation with the WHO-SSA for anti-pneumococcal antibody titers.
- The ECL-plex assay achieved 95% sensitivity and 84% specificity for SPAD diagnosis.
- The new assay demonstrated 89% agreement with the reference method in SPAD screening.

## Abstract

Streptococcus pneumoniae can be responsible for severe infections, especially in patients with primary antibody deficiencies like selective anti-polysaccharide antibodies deficiency (SPAD). The reference method recommaned by the World Health Organization for assessment of anti-pneumococcal capsular polysaccharides (PCPs) IgG antibodies is a standardized serotype-specific ELISA (WHO-SSA), but this manual method is time-consuming and limit the number of evaluated PCPs. We aim to evaluate the performance values of a multiplex assay based on electrochemiluminescence (ECL-plex). A panel of 164 sera from 82 patients sampled before and 4–8 weeks after immunization by the 23-valent pneumococcal polysaccharide vaccine (PPV23) were assessed by the reference WHO-SSA (7 to 13 serotypes) and by an 18-plex ECL assay (18 serotypes). All patients had normal serum Ig/subclasses levels and were classified as good (n = 43) or poor responders (n = 39, i.e. SPAD patients) according to the American Academy of Asthma, Allergy and Immunology’s (AAAAI) current guidelines. We observed excellent correlations between the two methods for anti-PCPs titers against 7 serotypes (r = 0.88 [95% CI: 0.87–0.90], n = 124 sera) and 13 serotypes (r = 0.87 [0.87–0.89], n = 40 sera). Using the AAAAI’s guidelines for interpretation, the test performance of the 18-plex ECL assay for SPAD diagnosis showed a sensitivity of 95% and specificity of 84%, positive and negative predictive values of 84% and 95%, respectively. The percentage of agreement was 89% between the SSA and the 18-plex ECL assay. The 18-plex ECL assay is a reliable, rapid, and simple method for evaluating anti-PCPs response and screening for SPAD diagnosis.

The online version contains supplementary material available at 10.1007/s10875-025-01911-0.