Haemoglobin production in the fetus and newborn

The most important difference between haemopoiesis in the fetus compared with postnatal life is the changing pattern of haemoglobin (Hb) production at each stage of development. The composition and names of these haemoglobins are shown in Table 22.1. Understanding the developmental changes in haemoglobin helps to explain the patterns of abnormal haemoglobin production in some inherited childhood anaemias. Embryonic haemoglobins (Hb Gower 1, Hb Gower 2 and Hb Portland) are produced between 4 and 8 weeks’ gestation, after which haemoglobin production switches to fetal haemoglobin (HbF). HbF is made up of 2 α chains and 2 γ chains (α₂γ₂) and is the main Hb during fetal life. HbF has a higher affinity for oxygen than adult Hb (HbA), and is therefore better able to hold on to oxygen, an advantage in the relatively hypoxic environment of the fetus (Fig. 22.1). At birth, the types of Hb are: HbF, HbA and HbA₂. HbF is gradually replaced by HbA and HbA₂ during the first year of life. By 1 year of age, the percentage of HbF is very low in healthy children and increased proportions of HbF are a sensitive indicator of some inherited disorders of haemoglobin production (haemoglobinopathies) .

Haematological values at birth and the first few weeks of life

Features are:

• At birth, the Hb in term infants is high, 14–21.5 g/dl, to compensate for the low oxygen concentration in the fetus. The Hb falls over the first few weeks, mainly due to reduced red cell production, reaching a nadir of around 10 g/dl at 2 months of age (Fig. 22.2). Normal haematological values at birth and during childhood are shown in the Appendix.

• Preterm babies have a steeper fall in Hb to a mean of 6.5–9 g/dl at 4–8 weeks chronological age.

• Normal blood volume at birth varies with gestational age. In healthy term infants the average blood volume is 80 ml/kg; in preterm infants the average blood volume is 100 ml/kg.

• Stores of iron, folic acid and vitamin B₁₂ in term and preterm babies are adequate at birth. However, in preterm infants, stores of iron and folic acid are lower and are depleted more quickly, leading to deficiency after 2–4 months if the recommended daily intakes are not maintained by supplements.

• White blood cell counts in neonates are higher than in older children (10–25 × 10⁹/L).

• Platelet counts at birth are within the normal adult range (150–400 × 10⁹/L).

Iron deficiency

The main causes of iron deficiency are:

Inadequate intake of iron is common in infants because additional iron is required for the increase in blood volume accompanying growth and to build up the child’s iron stores (Fig. 22.5). A 1-year-old infant requires an intake of iron of about 8 mg/day, which is about the same as his father (9 mg/day) but only half that of his mother (15 mg/day).

Iron may come from:

Iron deficiency may develop because of a delay in the introduction of mixed feeding beyond 6 months of age or to a diet with insufficient iron-rich foods, especially if it contains a large amount of cow’s milk (Box 22.1). Iron absorption is markedly increased when eaten with food rich in vitamin C (fresh fruit and vegetables) and is inhibited by tannin in tea.

Iron requirements during childhood

Red cell aplasia

There are three main causes of red cell aplasia in children:

The diagnostic clues to red cell aplasia are:

Diamond–Blackfan anaemia (DBA) is a rare disease (5–7 cases/million live births). There is a family history in 20% of cases; the remaining 80% are sporadic. Specific gene mutations in ribosomal protein (RPS) genes are implicated in some cases. Most cases present at 2–3 months of age, but 25% present at birth. Affected infants have symptoms of anaemia; some have other congenital anomalies, such as short stature or abnormal thumbs. Treatment is by oral steroids; monthly red blood cell transfusions are given to children who are steroid unresponsive and some may also be offered stem cell transplantation.

Transient erythroblastopenia of childhood (TEC) is usually triggered by viral infections and has the same haematological features as Diamond–Blackfan anaemia. The main differences between them is that, unlike Diamond–Blackfan anaemia, transient erythroblastopenia of childhood always recovers, usually within several weeks, there is no family history or RPS gene mutations and there are no congenital anomalies.

Hereditary spherocytosis

HS occurs in 1 in 5000 births in Caucasians. It usually has an autosomal dominant inheritance, but in 25% there is no family history and it is caused by new mutations. The disease is caused by mutations in genes for proteins of the red cell membrane (mainly spectrin, ankyrin or band 3). This results in the red cell losing part of its membrane when it passes through the spleen. This reduction in its surface-to-volume ratio causes the cells to become spheroidal, making them less deformable than normal red blood cells and leads to their destruction in the microvasculature of the spleen.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency

G6PD deficiency is the commonest red cell enzymopathy affecting over 100 million people worldwide. It has a high prevalence (10–20%) in individuals originating from central Africa, the Mediterranean, the Middle East and the Far East. Many different mutations of the gene have been described, leading to different clinical features in different populations.

G6PD is the rate-limiting enzyme in the pentose phosphate pathway and is essential for preventing oxidative damage to red cells. Red cells lacking G6PD are susceptible to oxidant-induced haemolysis. G6PD deficiency is X-linked and therefore predominantly affects males. Females who are heterozygotes are usually clinically normal as they have about half the normal G6PD activity. Females may be affected either if they are homozygous or, more commonly, when by chance more of the normal than the abnormal X chromosomes have been inactivated (extreme Lyonisation – the Lyon hypothesis is that, in every XX cell, one of the X chromosomes is inactivated and that this is random). In Mediterranean, Middle Eastern and Oriental populations, affected males have very low or absent enzyme activity in their red cells. Affected Afro-Caribbeans have 10–15% normal enzyme activity.

Haemoglobinopathies

These are red blood cell disorders which cause haemolytic anaemia because of reduced or absent production of HbA (α- and β-thalassaemias) or because of the production of an abnormal Hb (e.g. sickle cell disease). α-Thalassaemias are caused by deletions (occasionally mutations) in the α-globin gene. β-Thalassaemia and sickle cell disease are caused by mutations in the β-globin gene. Clinical manifestations of the haemoglobinopathies affecting the β-chain are delayed until after 6 months of age when most of the HbF present at birth has been replaced by adult HbA (Fig. 22.7, Table 22.2).

Table 22.2

Haemoglobins in haemoglobinopathies

	HbA	HbA2	HbF	HbS
Newborn	25%	1%	74%	−
Adult	97%	2%	−	−
β-Thalassaemia trait	>90%	↑	+ ↑	−
β-Thalassaemia major	−	↑	↑	−
Sickle cell trait			+ ↑
Sickle cell disease	−		+ ↑

Sickle cell disease

This is now the commonest genetic disorder in children in many European countries, including the UK (prevalence 1 in 2000 live births). Sickle cell disease is the collective name given to haemoglobinopathies in which HbS is inherited. HbS forms as a result of a point mutation in codon 6 of the β-globin gene, which causes a change in the amino acid encoded from glutamine to valine. Sickle cell disease is most common in patients whose parents are black and originate from tropical Africa or the Caribbean but it is also found in the Middle East and in low prevalence in most other parts of the world except for northern Europeans.

There are three main forms of sickle cell disease and the sickle trait:

Clinical features

These are listed in Figure 22.8.

SC disease

Children with SC disease usually have a nearly normal haemoglobin level and fewer painful crises than those with HbSS, but they may develop proliferative retinopathy in adolescence. Their eyes should be checked periodically. They are also prone to develop osteonecrosis of the hips and shoulders.

Sickle cell trait (AS)

This is asymptomatic and rarely causes problems except under conditions of low oxygen tension. General anaesthesia does not constitute a risk in this population as long as they have been identified and hypoxia avoided.

β-Thalassaemias

The β-thalassaemias occur most often in people from the Indian subcontinent, Mediterranean and Middle East (Fig. 22.12). In the UK, most affected children are born to parents from the Indian subcontinent; in the past, many were born to Greek Cypriots, but this has become uncommon through active genetic counselling within their community.

There are two main types of β thalassaemia – both of which are characterised by a severe reduction in the production of β-globin (and thereby reduction in HbA production). All affected individuals have a severe reduction in β-globin and disease severity depends on the amount of residual HbA and HbF production.

Management

The condition is uniformly fatal without regular blood transfusions, so all patients are given lifelong monthly transfusions of red blood cells. The aim is to maintain the haemoglobin concentration above 10 g/dl in order to reduce growth failure and prevent bone deformation. Repeated blood transfusion causes chronic iron overload, which causes cardiac failure, liver cirrhosis, diabetes, infertility and growth failure. For this reason, all patients are treated with iron chelation with subcutaneous desferrioxamine, or with an oral iron chelator drug, such as deferasirox, starting from 2 to 3 years of age. Patients who comply well with transfusion and chelation have a 90% chance of living into their forties and beyond. However, compliance is difficult. Those who cannot comply have a high mortality in early adulthood from iron overload. The complications of multiple transfusions are shown in Box 22.3. An alternative treatment for β-thalassaemia major is bone marrow transplantation, which is currently the only cure. It is generally reserved for children with an HLA-identical sibling as there is then a 90–95% chance of success (i.e. transfusion independence and long-term cure) but a 5% chance of transplant-related mortality.

Case History

22.2 Acute sickle chest syndrome

Princess, a 9-year-old girl with known sickle cell anaemia (HbSS), presented with increasing chest pain for 6 h. She had a non-productive cough. On examination, she had a fever of 39.7°C. Her breathing was laboured, respiratory rate increased and there was reduced air entry at both bases.

Investigations

• Haemoglobin 6 g/dl, WBC 14 × 10⁹/L, platelets 350 × 10⁹/L

• Chest X-ray (see Fig. 22.11)

• Oxygen saturation – 89% in air

• Arterial PO₂ – 9.3 kPa (70 mmHg) breathing face-mask oxygen

• Blood cultures were taken and viral titres performed.

A diagnosis of acute sickle chest syndrome was made, a potentially fatal condition. She was given oxygen by CPAP (continuous positive airways pressure). An exchange transfusion was performed. Broad-spectrum antibiotics were commenced. She responded well to treatment.

Clinical features and complications of β-thalassaemia major

Box 22.3

Complications of long-term blood transfusion in children

Iron deposition – the most important (all patients)

• Heart – cardiomyopathy

• Liver – cirrhosis

• Pancreas – diabetes

• Pituitary gland – delayed growth and sexual maturation

• Skin – hyperpigmentation

Antibody formation (10% of children)

• Allo-antibodies to transfused red cells in the patient make finding compatible blood very difficult

Infection – now uncommon (<10% of children)

• Hepatitis A, B, C

• HIV

• Malaria

• Prions (e.g. new variant CJD)

Venous access (common problem)

• Often traumatic in young children

• Central venous access device (e.g. Portacath) may be required; these predispose to infection.

β-Thalassaemia trait

Heterozygotes are usually asymptomatic. The red cells are hypochromic and microcytic. Anaemia is mild or absent, with a disproportionate reduction in MCH (18–22 fl) and MCV (60–70 fl). The red blood cell count is therefore usually increased (>5.5 × 10¹²/L). The most important diagnostic feature is a raised HbA₂, usually about 5%, and in about half there is a mild elevation of HbF level of 1–3%. β-Thalassaemia trait can cause confusion with mild iron deficiency because of the hypochromic/microcytic red cells but can be distinguished by measuring serum ferritin, which is low in iron deficiency but not β-thalassaemia trait.

To avoid unnecessary iron therapy, serum ferritin levels should be measured in patients with mild anaemia and microcytosis prior to starting iron supplements.

α-Thalassaemias

Healthy individuals have four α-globin genes. The manifestation of α-thalassaemia syndromes depends on the number of functional α-globin genes.

The most severe α-thalassaemia, α-thalassaemia major (also known as Hb Barts hydrops fetalis) is caused by deletion of all four α-globin genes, so no HbA (α₂β₂) can be produced. It occurs mainly in families of South-east Asian origin and presents in mid-trimester with fetal hydrops (oedema and ascites) from fetal anaemia, which is always fatal in utero or within hours of delivery. The only long-term survivors of α-thalassaemia major are those who have received monthly intrauterine transfusions until delivery followed by lifelong monthly transfusions after birth. The diagnosis is made by Hb electrophoresis or Hb HPLC (high-performance liquid chromatography), which shows only Hb Barts.

When only three of the α-globin genes are deleted (HbH disease), affected children have mild–moderate anaemia but occasional patients are transfusion-dependent.

Deletion of one or two α-globin genes (known as α-thalassaemia trait) is usually asymptomatic and anaemia is mild or absent. The red cells may be hypochromic and microcytic, which may cause confusion with iron deficiency.

Increased red cell destruction (haemolytic anaemia)

This occurs either because of an antibody destroying the red blood cells (i.e. an extrinsic cause) or because there is an intrinsic abnormality of the surface or intracellular contents of the red blood cell. The main causes of haemolytic anaemia in neonates are:

The diagnostic clues to a haemolytic anaemia are an increased reticulocyte count (due to increased red cell production to compensate for the anaemia) and increased unconjugated bilirubin (due to increased red cell destruction with release of this bile pigment into the plasma).

Haemolytic disease of the newborn (immune haemolytic anaemia of the newborn) is due to antibodies against blood group antigens. The most important are: anti-D (a ‘rhesus’ antigen), anti-A or anti-B (ABO blood group antigens) and anti-Kell. The mother is always negative for the relevant antigen (e.g. rhesus D-negative) and the baby is always positive; the mother then makes antibodies against the baby’s blood group and these antibodies cross the placenta into the baby’s circulation causing fetal or neonatal haemolytic anaemia. The diagnostic clue to this type of haemolytic anaemia is a positive direct anti-globulin test (Coombs test). This test is only positive in antibody-mediated anaemias and so is negative in all the other types of haemolytic anaemia. (These conditions are considered further in Chapter 10.)

The most common causes of non-immune haemolytic anaemia in neonates are: G6PD (glucose-6-phosphate dehydrogenase) deficiency and hereditary spherocytosis. Haemoglobinopathies, apart from α-thalassaemia, rarely present with clinical features in the neonatal period but are detected on neonatal haemoglobinopathy screening (Guthrie test).

Blood loss

The main causes are:

The main diagnostic clue is severe anaemia with a raised reticulocyte count and normal bilirubin.

Anaemia of prematurity

The main causes are:

Fanconi anaemia

This is the most common inherited form of aplastic anaemia. It is an autosomal recessive condition. The majority of children have congenital anomalies, including short stature, abnormal radii and thumbs, renal malformations, microphthalmia and pigmented skin lesions. Children may present with one or more of these anomalies or with signs of bone marrow failure which do not usually become apparent until the age of 5 or 6 years. Neonates with Fanconi anaemia nearly always have a normal blood count but it can be diagnosed by demonstrating increased chromosomal breakage of peripheral blood lymphocytes. This test can be used to identify affected family members or for prenatal diagnosis. Affected children are at high risk of death from bone marrow failure or transformation to acute leukaemia. The recommended treatment is bone marrow transplantation using normal donor marrow from an unaffected sibling or matched unrelated marrow donor.

Shwachman–Diamond syndrome

This rare autosomal recessive disorder is characterised by bone marrow failure, together with signs of pancreatic exocrine failure and skeletal abnormalities. Most are caused by mutations in the SBDS gene, which can be used for identifying unusual cases or prenatal diagnosis. The most common haematological problem is an isolated neutropenia or mild pancytopenia. Like Fanconi anaemia, there is an increased risk of transforming to acute leukaemia.

Normal haemostasis

Haemostasis describes the normal process of blood clotting. It takes place via a series of tightly regulated interactions involving cellular and plasma factors.

There are five main components:

1. Coagulation factors – are produced (mainly by the liver) in an inactive form and are activated when coagulation is initiated (usually by tissue factor (TF), which is released by vessel injury; see Fig. 22.14)

2. Coagulation inhibitors – these either circulate in plasma or are bound to endothelium and are necessary to prevent widespread coagulation throughout the body once coagulation has been initiated

3. Fibrinolysis – this process limits fibrin deposition at the site of injury due to activity of the key enzyme plasmin

4. Platelets – are vital for haemostasis as they aggregate at sites of vessel injury to form the primary haemostatic plug which is then stabilised by fibrin

5. Blood vessels – both initiate and limit coagulation. Intact vascular endothelium secretes prostaglandin I₂ and nitric oxide (which promote vasodilatation and inhibit platelet aggregation). Damaged endothelium releases TF and procoagulants (e.g. collagen and von Willebrand factor) and there are inhibitors of coagulation on the endothelial surface (thrombomodulin, antithrombin and protein S) to modulate coagulation.

The endpoint of the coagulation cascade is generation of thrombin. A simplified model is shown in Figure 22.14. The two main pathways for thrombin generation were identified many years ago as the intrinsic and extrinsic pathways. Important components of these pathways are still being discovered. In recent years, the crucial role of tissue factor (TF) in haemostasis has been recognised and it is now thought that the extrinsic pathway is the one primarily responsible for initiating both normal haemostasis and thrombotic disease.

Clinical features

The disorder is graded as severe, moderate or mild, depending on the FVIII:C (or IX:C in haemophilia B) level (Table 22.4). The hallmark of severe disease is recurrent spontaneous bleeding into joints and muscles, which can lead to crippling arthritis if not properly treated (Fig. 22.16). Most children present towards the end of the first year of life, when they start to crawl or walk (and fall over). Bleeding episodes are most frequent in joints and muscles. Where there is no family history, non-accidental injury may initially be suspected. Almost 40% of cases present in the neonatal period, particularly with intracranial haemorrhage, bleeding post-circumcision or prolonged oozing from heel stick and venepuncture sites. The severity usually remains constant within a family.

Management

Recombinant FVIII concentrate for haemophilia A or recombinant FIX concentrate for haemophilia B is given by prompt intravenous infusion whenever there is any bleeding. If recombinant products are unavailable, highly purified, virally inactivated plasma-derived products should be used. The quantity required depends on the site and nature of the bleed. In general, raising the circulating level to 30% of normal is sufficient to treat minor bleeds and simple joint bleeds. Major surgery or life-threatening bleeds require the level to be raised to 100% and then maintained at 30–50% for up to 2 weeks to prevent secondary haemorrhage. This can only be achieved by regular infusion of factor concentrate (usually 8–12-hourly for FVIII, 12–24-hourly for FIX, or by continuous infusion) and by closely monitoring plasma levels. Intramuscular injections, aspirin and non-steroidal anti-inflammatory drugs should be avoided in all patients with haemophilia.

Complications are listed in Box 22.5.

Home treatment is encouraged to avoid delay in treatment, which increases the risk of permanent damage, e.g. progressive arthropathy. Parents are usually taught to give replacement therapy at home when the child is 2–3 years of age and many children are able to administer their own treatment from 7–8 years of age.

Prophylactic FVIII is given to all children with severe haemophilia A to further reduce the risk of chronic joint damage by raising the baseline level above 2%. Primary prophylaxis usually begins at age 2–3 years, and is given two to three times per week. If peripheral venous access is poor, a central venous access device (e.g. Portacath) may be required. Prophylaxis has been shown to result in better joint function in adult life. Similarly, patients with severe haemophilia B are usually given prophylactic FIX.

Desmopressin (DDAVP) may allow mild haemophilia A to be managed without the use of blood products. It is given by infusion and stimulates endogenous release of FVIII:C and von Willebrand factor (vWF). Adequate levels can be achieved to enable minor surgery and dental extraction to be undertaken. DDAVP is ineffective in haemophilia B.

Haemophilia centres should supervise the management of children with bleeding disorders. They provide a multidisciplinary approach with expert medical, nursing and laboratory input. Specialised physiotherapy is needed to preserve muscle strength and avoid damage from immobilisation. Psychosocial support is an integral part of maintaining compliance.

Self-help groups such as the Haemophilia Society may provide families with helpful information and support.

Clinical features

These are:

In contrast to haemophilia, spontaneous soft tissue bleeding such as large haematomas and haemarthroses are uncommon.

Management

Treatment depends on the type and severity of the disorder. Type 1 vWD can usually be treated with DDAVP, which causes secretion of both FVIII and vWF into plasma. DDAVP should be used with caution in children <1 year of age as it can cause hyponatraemia due to water retention and may cause seizures, particularly after repeated doses, and if fluid intake is not strictly regulated. More severe types of vWD have to be treated with plasma-derived FVIII concentrate, as DDAVP is ineffective and recombinant FVIII concentrate contains no vWF. Cryoprecipitate is no longer used to treat vWD as it has not undergone viral inactivation. Intramuscular injections, aspirin and non-steroidal anti-inflammatory drugs should be avoided in all patients with vWD.

Immune thrombocytopenia (ITP)

Immune thrombocytopenia is the commonest cause of thrombocytopenia in childhood. It has an incidence of around 4 per 100 000 children per year. It is usually caused by destruction of circulating platelets by anti-platelet IgG autoantibodies. The reduced platelet count may be accompanied by a compensatory increase of megakaryocytes in the bone marrow.

Management

In about 80% of children, the disease is acute, benign and self-limiting, usually remitting spontaneously within 6–8 weeks. Most children can be managed at home and do not require hospital admission. Treatment is controversial. Most children do not need any therapy even if their platelet count is <10 × 10⁹/L but treatment should be given if there is evidence of major bleeding (e.g. intracranial or gastrointestinal haemorrhage) or persistent minor bleeding that affects daily lives such as excessive epistaxis or menstrual bleeding. The treatment options include oral prednisolone, intravenous anti-D or intravenous immunoglobulin and all have significant side-effects. Platelet transfusions are reserved for life-threatening haemorrhage as they raise the platelet count only for a few hours. The parents need immediate 24-hour access to hospital treatment, and the child should avoid trauma, as far as possible, and contact sports while the platelet count is very low.

Case History

22.3 Immune thrombocytopenic purpura (ITP)

Sian, aged 5 years, developed bruising and a skin rash over 24 h. She had had an upper respiratory tract infection the previous week. On examination she appeared well but had a purpuric skin rash with some bruises on the trunk and legs (Fig. 22.17). There were three blood blisters on her tongue and buccal mucosa, but no fundal haemorrhages, lymphadenopathy or hepatosplenomegaly. Urine was normal on dipsticks testing. A full blood count showed Hb 11.5 g/dl with normal indices, WBC and differential normal, platelet count 17 × 10⁹/L. The platelets on the blood film were large; the film was otherwise normal. A diagnosis of ITP was made and she was discharged home. Her parents were counselled and given emergency contact names and telephone numbers. They were also given literature on the condition and advised that she should avoid contact sports but should continue to attend school. Over the next 2 weeks she continued to develop bruising and purpura but was asymptomatic. By the third week, she had no new bruises, and her platelet count was 25 × 10⁹/L; the blood count and film showed no new abnormalities. The following week, the platelet count was 74 × 10⁹/L and a week later it was 200 × 10⁹/L. She was discharged from follow-up.

In immune thrombocytopenic purpura, in spite of impressive cutaneous manifestations and extremely low platelet count, the outlook is good and most will remit quickly without any intervention.

Diagnosis

Although inherited thrombophilia is very uncommon, these disorders predispose to life-threatening thrombosis and so it is important not to miss the diagnosis in any child presenting with an unexplained thrombotic event. Therefore, screening tests for the presence of an inherited thrombophilia should be carried out in the following situations:

The screening tests are assays for proteins C and S, antithrombin assay, polymerase chain reaction (PCR) for factor V Leiden and for the prothrombin gene mutation.

Mutations in factor V (factor V Leiden) and the prothrombin gene, respectively, are present in 5% and 2% of the northern European population. Children with protein C deficiency or factor V Leiden have 4–6 times higher risk of developing recurrent thromboses. The risk increases significantly if these conditions are inherited together. Therefore it is reasonable to screen children who develop thrombosis for all of these factors in order to plan the best management to prevent thrombosis. In the UK, current practice is not to screen asymptomatic children for genetic defects, which are not going to affect their medical management, e.g. on the basis of family history alone, until they are old enough to receive appropriate counselling and make decisions for themselves.