Читать книгу Neonatal Haematology - Barbara J. Bain, Irene Roberts - Страница 23

The reticulocyte count falls rapidly after birth as erythropoiesis declines. In term babies it then starts to increase at 7–8 weeks of age, reaching 35–200 × 10⁹/l (1–1.8%) at 2 months of age; in preterm babies it increases at 6–8 weeks of age.³⁵ Neonatal reticulocytes, like mature neonatal red blood cells, have a larger volume and lower Hb than adult reticulocytes.³⁵ Manual reticulocyte counts have now largely been replaced by automated reticulocyte counts based on cell size and ribonucleic acid (RNA) content. Automated reticulocyte counts also provide a measure of the fraction of reticulocytes with the highest RNA content (Immature Reticulocyte Fraction [IRF]), which has been used in neonates to determine whether or not there is increased erythropoietic activity, for example in response to EPO treatment or as a diagnostic aid to haemolysis.^72–74

Normal ranges for the numbers of circulating nucleated red blood cells (NRBC) in neonates have been compiled by Christensen et al.⁶⁶ and are generally higher in preterm neonates (2–3 × 10⁹/l) than in term neonates (about 1 × 10⁹/l) (see Table 1.2). Although modern analysers are increasingly able to generate accurate absolute NRBC counts, a useful guide from examination of blood films is that the presence of up to 5 NRBC/100 white blood cells in a term baby and up to 25 NRBC/100 white blood cells in a preterm baby can be considered normal for the first 1–2 days of life. In fact, there seems to be no difference between results obtained when the manual and automated methods are compared.⁷⁵ The number of NRBC in the peripheral blood falls rapidly over the first week of life and these cells are no longer seen after the second week of life. By contrast, circulating erythroblasts are increased in a variety of conditions in neonates and their presence can therefore be useful diagnostically because they usually indicate increased erythropoiesis driven either by anaemia or by chronic intrauterine hypoxia, for example due to IUGR (Table 1.4 and Fig. 1.10). It should be noted that NRBC also appear in the peripheral blood as part of a leucoerythroblastic picture, most typically in response to acute perinatal hypoxia (Fig. 1.11).^76,77