Association between red blood cell distribution width coefficient of variation and post-treatment bilirubin decline velocity in neonatal hyperbilirubinemia

Background Red blood cell distribution width coefficient of variation (RDW-CV) reflects erythrocyte heterogeneity, but its correlation with posttreatment bilirubin kinetics in neonatal hyperbilirubinemia (NHB) remains underexplored. Methods This cross-sectional study analyzed 803 neonates (≥35 weeks of gestation) with NHB. RDW-CV was measured at admission, and bilirubin decline velocity was calculated during phototherapy. Associations were evaluated using multivariate linear regression and restricted cubic splines, adjusted for demographic, maternal, and hematologic factors. Results Each 1% RDW-CV increase independently reduced bilirubin decline velocity by 2.04 μmol/(L·day) ( β = −2.04, 95% CI: −3.48∼−0.60, P = 0.006). Compared with neonates in the lowest RDW-CV tertile (11.9 to <14.6%), those in the highest tertile (15.2%–20.8%) exhibited a significant reduction in bilirubin decline velocity of 5.33 μmol/(L·day) ( β = −5.33, 95% CI: −8.44 to −2.21, P = 0.001). A linear dose–response trend ( P = 0.001) was confirmed. Subgroup analyses confirmed consistent associations across neonatal sex, maternal age, and major pregnancy complications (all P for interaction > 0.05). Conclusions RDW-CV is an independent predictor of bilirubin clearance in NHB, exhibiting a linear dose–response effect. These findings highlight its potential as a biomarker for phototherapy stratification.