Interaction of physical contact level and team modality in modulating serum immunoglobulin A concentration in elite athletes: a cross-sectional study

BACKGROUND: Serum immunoglobulin A (IgA) concentration is an important yet controversial marker of immune status in athletes. Data on its concentration the off-season and the influence of factors such as the level of physical contact and the individual/team nature of the sport are scarce. AIM: To evaluate the combined effect of the level of physical contact (contact vs low-contact) and sport modality (individual vs team) on serum IgA concentration in elite athletes during the off-season period. METHODS: A retrospective, cross-sectional study was conducted using anonymized data from 12,317 Russian national team athletes in boxing, tennis, basketball, and volleyball from 2012–2020. Groups were formed using a 2×2 factorial design: "contact" (boxing, basketball) vs "low-contact" (tennis, volleyball) and "individual" (boxing, tennis) vs "team" (basketball, volleyball) modality. RESULTS: Statistically significant differences were found in the median serum IgA concentrations, with all values remaining within the reference range. Athletes in contact sports (basketball: 1.81 g/L; boxing: 1.72 g/L) had significantly higher IgA levels than athletes in low-contact disciplines (volleyball: 1.57 g/L; tennis: 1.55 g/L). The factor analysis mathematically confirmed the existence of two independent constructs differentiated on the basis of physical contact. No significant effect of sport modality (individual/team) or factor interaction was observed. CONCLUSION: In the inter-competitive phase, the degree of physical contact acts as a key determinant modulating basal serum IgA within physiological limits, with elevated concentrations observed in contact sport athletes. The practical significance of these findings lies in the necessity of a sport-specific approach to immunological monitoring: the lower bound of the reference range considered normal for low-contact disciplines may be inadequate for athletes practicing contact-intensive sports.