Reference ranges for blood concentrations of nucleated red blood cells in neonates.

Background: Previous studies reported a relationship between high nucleated red blood cells (NRBC) in neonates and the development of intraventricular hemorrhage (IVH) and/or retinopathy of prematurity (ROP).

Objective: We sought to (1) establish reference ranges for NRBC in neonates based on a large data set, (2) compare NRBC from automated versus manual counts, (3) determine the effect of an elevated NRBC, on the day of birth, on the odds of developing grade ≥3 IVH or ROP.

Methods: We analyzed all NRBC obtained during 8.5 years in a multihospital system, displaying the 5th and 95th percentile limits according to gestational age and postnatal age.

Results: NRBC counts were retrieved from 61,932 neonates, 26,536 of which were excluded from the data set. Comparing 9,000 samples run simultaneously on manual versus automated methods, the manual counts yielded slightly higher counts, but the difference is likely insignificant clinically. Altitude of the birth hospital did not correlate with NRBC, and no correlations were observed with cord pH or 1- or 5-min Apgar. An NRBC count >95th percentile limit was associated with higher odds of developing a grade ≥3 IVH (OR 4.28; 95% CI 3.17-5.77) and grade ≥3 ROP (OR 4.18; 95% CI 2.74-6.38).

Conclusion: The figures of this report display reference ranges for NRBC according to gestational age and postnatal age. An NRBC count above the 95% limit at birth is associated with a higher risk of subsequently developing severe IVH and severe ROP. We speculate that this association is because an elevated NRBC count is a marker for prenatal hypoxia.