Determination and verification of reference intervals of serum immunoglobulin G at birth.

Background: To accurately assess hypogammaglobulinemia at birth, it is essential to determine the reference intervals of serum immunoglobulin (IgG) levels in newborns. In the present study, we determined the gestational age (GA)-/birth weight (BW)-dependent percentile-based reference intervals of serum IgG levels and converted them into simple formulas for practical use.

Methods: Serum IgG levels were measured in cord blood from 2902 newborns delivered at 22 to 41 weeks of GA or 264 to 4642 g of BW after exclusion of those with congenital disorders. Linear regression analysis was used to correlate GA and UC-IgG levels and BW and UC-IgG levels. After calculation of the percentile values of UC-IgG levels for each GA or BW, the distributions were approximated by the least-squares method. Fitness was evaluated by the coefficient of determination (R²).

Results: Significant positive correlations were found both between GA and UC-IgG levels (r_s = 0.790, P < 0.001) and BW and UC-IgG levels (r_s = 0.626, P < 0.001). The distribution of the 5%ile of UC-IgG levels (Y) by GA or BW (X) was approximated as a straight line (Y = 37.5 *X - 775.8; Y = 0.161 *X + 95.34, respectively). The fitness was stronger in the GA-derived formula than the BW-derived formula (R² = 0.973 vs 0.913).

Conclusions: We established GA-/BW-dependent reference percentile-based intervals for serum IgG levels using cord blood from 2902 newborns without congenital disorders. Using GA-dependent reference intervals may be useful for assessing hypogammaglobulinemia at birth.