The authors aimed to determine whether their reticulated platelet percentage (RP%) analysis technique was suitable for use in term and preterm neonates and to characterize RP% values among nonthrombocytopenic neonates.
The authors modified a whole blood method that uses dual-color CD41 staining for platelet gating and thiazole orange for RNA content, combined with RNase treatment of half the sample to subtract non-RNA fluorescence. The RP% was measured in samples from 10 healthy adults and then a longitudinal study was performed in 15 nonthrombocytopenic preterm neonates on days of life 0 to 1, 2 to 5, 6 to 10, and then weekly until day 28. The authors also performed a cross-sectional study of RP% in 22 nonthrombocytopenic neonates of different gestational age (GA) and postconceptional age (PCA).
Overall, neonates had a higher RP% (2.7 ± 1.6%) than adults (1.1 ± 0.5%; P < 0.01). In preterm neonates, an increase in the RP% occurred between days 0 and 1 (3.3 ± 1.3%) and days 2 and 5 (5.1 ± 1.8%; P = 0.003). By days 6 to 10, the RP% decreased to 3.2 ± 1.1% and remained unchanged throughout the rest of the study period. In neonates less than 7 days old, an inverse relationship was observed between RP% and GA (n = 20, r = −0.70; P = 0.0005). A correlation between RP% and PCA was not seen in neonates 7 days of age or older.
This method for determining RP% is suitable for use in term and preterm neonates. In preterm infants, the RP% significantly increases over the first 2 to 5 days of life and then decreases to a stable level over the first 28 days. RP% is generally higher in neonates than in adults. Among preterm infants in the first week of life, the RP% is inversely related to GA.
From the *Division of Neonatology, Department of Pediatrics, University of Florida College of Medicine, Gainesville, Florida; †Department of Biostatistics, University at Buffalo, Buffalo, New York; ‡Division of Neonatology and Department of Pediatrics, University of South Florida, St. Petersburg, Florida; and §Department of Pathology, University of Arizona, Tucson, Arizona.
Received for publication January 12, 2004; accepted October 4, 2004.
Supported by grants HL69990 and RR-00082 from the National Institutes of Health, a grant from the American Heart Association, Florida Affiliate, and a grant from the Children's Miracle Network Telethon.
Reprints: Matthew A. Saxonhouse, MD, Division of Neonatology, University of Florida, College of Medicine, P.O. Box 100296, Gainesville, FL 32610-0296 (e-mail: Saxonma@peds.ufl.edu).