Читать книгу Neonatal Haematology - Barbara J. Bain, Irene Roberts - Страница 19

Neonatal red blood cells, particularly in preterm babies, have a shorter lifespan than adult red blood cells. Red cell lifespan is inversely proportional to gestational age at birth. Studies over 50 years ago using isotopically labelled red blood cells estimated red blood cell lifespans for preterm infants at 35–50 days, compared with 60–70 days for term infants and 120 days for healthy adults.³⁵ More recent estimates, using mathematical modelling and transfusion of autologous cord blood cells, have also calculated the red cell lifespan in preterm neonates to be approximately 50 days.⁴³

The reasons for a lower red cell lifespan in neonates, although not fully understood, are thought to include the many biochemical and functional differences in the membrane of neonatal versus adult red blood cells (see Table 1.1). Known differences between neonatal and adult red blood cells include increased resistance to osmotic lysis, increased mechanical fragility, increased total lipid content with an altered lipid profile, increased insulin‐binding sites and reduced expression of blood group antigens such as A, B and I.³⁵ Together these differences translate into the characteristic morphological differences seen in neonatal blood films, particularly in preterm neonates (Figs 1.7–1.9), and are associated with accelerated red cell membrane loss⁴⁴ leading to reduced red cell lifespan. Indeed, the distinctive geometry of neonatal red blood cells and the membrane deformability of some of the irregularly shaped cells have been compared to the properties of red blood cells in the inherited red cell membrane disorders.⁴⁵

Fig. 1.7 Normal blood film at term. MGG, ×40.

Fig. 1.8 Normal preterm red cells at different gestational ages: (a) baby born at 28 weeks’ gestation showing echinocytes, polychromatic macrocytes and one nucleated red blood cell (NRBC); (b) baby born at 25 weeks’ gestation showing numerous echinocytes, echinocytic fragments and one NRBC. Note that anisocytosis and poikilocytosis is greater at 25 weeks than at 28 weeks. MGG, ×100.

Fig. 1.9 Blood film of a normal preterm baby (born at 28 weeks’ gestation) showing a degree of erythroblastosis. MGG, ×40.