Relevance of circulating
IgG
levels as a marker of health in plasma donors
Audrey Laforce‐Lavoie, Jessyka Deschênes, Marc Cloutier, Antoine Lewin, Renée Bazin Abstract
Background
Frequent plasma donation is associated with reduced circulating IgG levels, prompting many jurisdictions to apply IgG‐based deferral thresholds as a precautionary donor‐safety measure. However, whether low IgG in healthy individuals reflects clinically meaningful immunosuppression remains unclear. This study evaluated IgG as a marker for donor health by integrating immunological, behavioral and self‐reported outcomes, including vaccine responses, return to donation, and health problems.
Study Design and Methods
The kinetics of IgG decline associated with frequent plasma donation were analyzed over 18 months in 49 first‐time and 50 repeat donors. Vaccine responses were evaluated in repeat donors with low or high IgG using ELISA to measure SARS‐CoV‐2 Spike receptor‐binding domain antibodies and avidity after primary and booster COVID‐19 vaccination. Return to plasma donation was examined in 3897 first‐time plasma donors followed up to 22 months. Self‐reported health problems were analyzed in 5347 plasma donors over 10 years.
Results
IgG levels declined during early donations in first‐time donors but stabilized thereafter, suggesting a new homeostatic set point rather than progressive IgG depletion. All vaccinated donors seroconverted after primary vaccination regardless of IgG level. Although antibody levels were slightly lower in low‐IgG donors, affinity maturation was comparable after boosting. IgG levels were not associated with return to donation or increased self‐reported health problems.
Discussion
Low IgG levels in healthy plasma donors were not associated with impaired immunity, donor retention, or increased self‐reported health problems. These findings support cautious interpretation of isolated IgG values in donor management and favor longitudinal monitoring over fixed thresholds.