Normal values

It is important to appreciate that the normal ranges for many haematological tests vary with age. Table 45.1 illustrates reference values for the total white cell count (WCC) and the differential count in children. More detailed listings of normal ranges of laboratory tests in childhood can be found in specialised paediatric haematology texts.

Neonatal disorders

Haemolytic disease of the newborn

Haemolytic disease of the newborn (HDN) is a disease of the fetus and newborn child. The haemolysis is caused by maternal IgG antibodies traversing the placenta and attaching to fetal red cells which are destroyed in the child’s reticuloendothelial system. The antibodies are directed against a fetal red cell antigen not shared by the mother. Incompatibility for one of a large number of different red cell blood group systems can cause HDN but most cases of clinically significant disease affect a Rhesus (Rh)D-positive child where the mother is RhD negative. Sensitisation of the mother (i.e. the formation of anti-D) occurs following the haemorrhage of fetal red cells into the maternal circulation. This usually occurs at parturition following a normal pregnancy but may also arise earlier in pregnancy or following abortion. ABO incompatibility between mother and fetus gives some protection against sensitisation to RhD as fetal red cells are quickly destroyed by the mother’s naturally occurring anti-A or anti-B antibodies. Unfortunately, in most cases baby and mother are ABO compatible. With the considerable success of prophylaxis against HDN due to RhD incompatibility (see below), the most common cause of the disorder is the formation of immune antibodies against ABO; most cases are associated with only mild haemolysis.

Diagnosis

Severe HDN can result in intrauterine death. In the newborn child the presentation is entirely dependent on the degree of haemolysis but common features include anaemia, jaundice, oedema and hepatosplenomegaly. High levels of circulating unconjugated bilirubin may lead to high frequency deafness or deposition in the basal ganglia with spasticity and other neurological symptoms and signs (‘kernicterus’). Further investigation of the anaemia reveals features typical of haemolysis (Fig 45.1) with a positive direct antiglobulin test (DAT). In HDN due to RhD incompatibility the baby is RhD positive and the mother RhD negative with a high level of anti-D.

Fig 45.1 Peripheral blood film in a newborn child with severe HDN.
Note the numerous nucleated red cells and polychromasia.

Management

Management of HDN is complex, requiring close liaison between the haematology laboratory and obstetrician. In RhD alloimmunisation, if maternal anti-D levels are high and paternal testing indicates RhD heterozygosity, the fetal Rh genotype can be determined non-invasively by applying PCR technology to a maternal blood sample. Another advance is velocimetry of the fetal middle cerebral artery during an affected pregnancy. High peak systolic velocities predict severe fetal anaemia and allow the selective use of more invasive techniques such as fetal blood sampling and intrauterine transfusion. Newborns may experience ongoing anaemia and require exchange transfusion. Later anaemia may respond to erythropoietin therapy. With optimal management, a healthy child is the outcome in more than 90% of cases.

RhD prophylaxis in RhD-negative mothers

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