Nucleated Red Blood Cells and the Risk of Mortality in Premature Infants; Application of Accelerated Failure Time Models

Background: Nucleated red blood cells (nRBCs) are infrequently observed in the peripheral blood of healthy infants, adults, and elderly individuals. Studies have indicated that the presence of these cells in the peripheral blood of premature infants suggests intrauterine hypoxia. Objectives: This study aims to determine the association between nRBCs in the peripheral blood of premature infants and outcomes, specifically mortality, using accelerated failure time (AFT) models. Methods: This registry-based, single-center cohort study was conducted on premature infants between March 5,2019, and September 10,2020, at a university hospital in Ilam, southwest Iran. A total of 450 premature infants were included in the study. Accelerated failure time models were applied to the dataset, and their performance was evaluated using visual Cox-Snell residuals and Akaike’s information criterion (AIC). Results: In the adjusted model, the Weibull model results indicated that the presence of nRBCs [adjusted time ratio (TR) 1.05, 95% CI: 1.01 - 1.08, P = 0.04] was a significant factor accelerating progression to death in premature infants. Conclusions: The presence of nRBCs is a risk factor for mortality in premature infants. Counting nRBCs on the first day of birth in premature infants could serve as a simple, accessible, cost-effective, and prognostic factor for mortality and morbidity related to retinopathy of prematurity (ROP), bronchopulmonary dysplasia (BPD), and intraventricular hemorrhage (IVH).