Assessing humoral immunity in daily practice: A retrospective study in a pediatric tertiary center.

The evaluation of humoral immunity is usually performed through the assessment of serum immunoglobulin levels, vaccine titer responses, and B-cell enumeration and phenotyping. We performed a retrospective study assessing humoral immunity in 469 pediatric patients referred at the Sainte-Justine University Hospital Center. Almost half of the patients had at least one abnormal humoral immunological parameter at their evaluation, with low vaccine response titer to protein antigen being the most frequent. Fifteen patients (3.2 %) had a proven monogenic IEI, and 21 patients (4.5 %) required Ig replacement. Besides the infectious burden, hypoIgG remains the only parameter associated with Ig replacement therapy after the age of 6 years. Low antibody titers against conjugate vaccines had low sensitivity and positive predictive values for starting Ig replacement. Our study highlights the challenge of evaluating the humoral function in the pediatric population with suspected IEI with significant age and sex-dependent variability between parameters.