The absolute nucleated red blood cell (aNRBC) count at birth is not an indicator for retinopathy of prematurity (ROP)

To establish the reproducibility of a published observation by Lubetzky et al. that infants affected by retinopathy of prematurity (ROP) had higher absolute nucleated red blood cell (aNRBC) counts than those unaffected. The authors suggested that infants exposed to intrauterine hypoxia are at higher risk for ROP. We attempted to verify this reported relationship of ROP with the aNRBCs at birth and hypothesized that infants with ROP ≥ stage 2 have higher aNRBCs at birth.

We report a retrospective 1:1 case matched analysis where cases had a diagnosis of grade II ROP or worse and matching infants had confirmed stage I or no ROP. Eligible infants had birth weights of 501 to 1500 g and were discharged alive from 1st January 2000 to 31st December 2008. Wilcoxon's signed rank test was performed for continuous comparisons. This study was approved by two local Institutional Review Boards.

In all, 66 matched pairs were analyzed. When comparing aNRBCs there was no statistically significant relationship (w=-0.265, P=0.791) between the ROP affected group (M=4550, s.d.=7342) and the unaffected group (M=5287, s.d.=6524).

We are unable to support the previously reported relationship of aNRBCs with ROP. Our population was three times larger, had higher aNRBCs and less retinopathy than previously reported. A biological principle of cause and effect or predisposition to ROP as reflected by aNRBCs should have been easier for us to demonstrate, if it existed.