Interpretability of Paired Pneumococcal Serotype-Specific IgG Testing in Adults With Solid Tumors: A Retrospective Chart-Review Cohort Study

BackgroundPaired pneumococcal serotype-specific immunoglobulin G (IgG) testing may be used when evaluating adults with solid tumors and suspected antibody deficiency, but interpretation depends on vaccine product, vaccination timing, treatment exposures, and clinical context.We assessed how often paired pneumococcal serology records met technical criteria for interpretation and how serologic classification varied according to vaccine product and threshold convention. Materials and methodsAdults with a solid tumor and at least two pneumococcal serotype-specific IgG panels were identified in the Mayo Clinic Enterprise Data Warehouse.All 108 patient charts were manually reviewed for vaccine product, documented administration between the paired panels, quantitative immunoglobulins, and relevant treatment exposures.A threshold of 1.3 µg/mL was used after the 23-valent pneumococcal polysaccharide vaccine (PPSV23), and after conjugate vaccination, 0.35 µg/mL was used descriptively as a population-level correlate of protection and not as a diagnostic threshold for specific antibody deficiency (SAD).The technical interpretability framework required a known vaccine product, vaccination documented between the paired panels, post-vaccination sampling four to 12 weeks after vaccination, and no major treatment confounder.Technical eligibility for assessment of polysaccharide antibody responsiveness additionally required PPSV23. ResultsOf the 407 patients with eligible solid tumors, 108 had at least two pneumococcal serotype-specific IgG panels and formed the analytic cohort.Vaccine product was identified in 101 patients (93.5%): 60 received PPSV23 and 41 received a conjugate vaccine.Applying a fixed 1.3 µg/mL threshold across vaccine products classified 49 of 108 patients (45.4%) below the specified serologic threshold, whereas descriptive productspecific thresholds classified 31 of 101 patients (30.7%) with a known vaccine product below the corresponding threshold; and 16 conjugate-vaccine recipients were reclassified as meeting the descriptive product-specific threshold.Vaccination was documented between the index panels in 53 patients (49.1%).Across the full cohort, 53 of 108 patients (49.1%) had at least one major treatment confounder, including 22 (20.4%)who received immunoglobulin replacement.Twelve paired-panel records (11.1%) met all four technical criteria; and nine involved PPSV23 and were therefore technically eligible for assessment of polysaccharide antibody responsiveness. ConclusionsOnly nine of 108 paired-panel records (8.3%) met all technical criteria and involved PPSV23.This finding reflects limitations in the interpretability of available testing records and does not estimate the prevalence of SAD.Clinical SAD could not be established because compatible recurrent infection history was not systematically captured and prior pneumococcal vaccination history was incompletely characterized.Clearer documentation of vaccine product and administration date, relevant treatment exposures, and appropriately timed postvaccination testing may improve the interpretability of pneumococcal antibody assessment in clinical practice.