Читать книгу Neonatal Haematology - Barbara J. Bain, Irene Roberts - Страница 27

The leucocytes that form the human blood and immune system in the developing fetus start to appear in the peripheral blood during the first trimester.⁹³ Monocytes and lymphocytes appear in fetal blood by 8 weeks post‐conception, although initially in very low numbers. This is followed by the appearance of neutrophils and eosinophils from around 14–16 weeks post‐conception, once haemopoiesis begins to be established in the bone marrow,^9,16 increasing by the end of the third trimester to the lower end of the values reported for leucocyte counts in term neonates. Blast cells are a normal feature in fetal blood, particularly in the second trimester, but are not usually greater than 10%.⁹⁴

Apart from alterations in the numbers of white blood cells in response to infection, leucocyte disorders are not common in neonates. Nevertheless, some diagnostic dilemmas do present in the neonatal period, particularly when there is neutropenia or a rare disorder such as congenital leukaemia is suspected. Careful evaluation of leucocyte morphology can not only help to make an early diagnosis of bacterial infection but can also suggest the type of bacterial infection and provide rapid clues to the presence of congenital viral infection or a rare genetic or metabolic disorder (see Chapter 3). In addition, automated leucocyte differential counts are often inaccurate in neonatal samples, particularly in very preterm neonates, so that validation from a blood film is important.

In contrast to the gestation‐related differences in red cell morphology, leucocyte morphology (neutrophils, monocytes, eosinophils, basophils and lymphocytes) is the same in healthy neonates of any gestation as in adults.