Hemolytic anemia in children

Hemolytic anemia in children accounts for about 5.3% of other blood diseases, and 11.5% of anemic conditions. Hereditary forms of diseases predominate in the structure of hemolytic anemias.

Hemolytic anemia is a group of diseases most characteristic of which is increased destruction of red blood cells due to a reduction in their lifespan. It is known that the normal lifespan of red blood cells is 100-120 days; about 1% of red blood cells are removed from the peripheral blood daily and replaced by an equal number of new cells coming from the bone marrow. This process creates a dynamic equilibrium under normal conditions, ensuring a constant number of red blood cells in the blood. With a reduction in the lifespan of red blood cells, their destruction in the peripheral blood is more intense than their formation in the bone marrow and release into the peripheral blood. In response to a reduction in the lifespan of red blood cells, bone marrow activity increases 6-8 times, which is confirmed by reticulocytosis in the peripheral blood. Continuing reticulocytosis in combination with some degree of anemia or even a stable hemoglobin level may indicate the presence of hemolysis.

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What causes hemolytic anemia?

Acute hemoglobinuria

1. Transfusion of incompatible blood
2. Medicines and chemical agents
   1. Chronically causing hemolytic anemia drugs: phenylhydrazine, sulfones, phenacetin, acetanilide (high doses) chemicals: nitrobenzene, lead toxins: snake and spider bites
   2. Periodically causing hemolytic anemia:
      1. Associated with G6PD deficiency: antimalarial (primaquine); antipyretics (aspirin, phenacetin); sulfonamides; nitrofurans; vitamin K; naphthalene; favism
      2. Associated with HbZurich: sulfonamides
      3. In case of hypersensitivity: quinine; quinidine; para-aminosalicylic acid; phenacetin
3. Infections
   1. bacterial: Clostridium Perfringens; Bartonella bacilliformis
   2. parasitic: malaria
4. Burns
5. Mechanical (eg artificial valves)

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Chronic hemoglobinuria

1. Paroxysmal cold hemoglobinuria; syphilis;
2. Idiopathic paroxysmal nocturnal hemoglobinuria
3. March hemoglobinuria
4. In hemolysis caused by cold agglutinins

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Pathogenesis of hemolytic anemia

Patients with hemolytic anemia with compensatory hyperplasia of the erythroid germ may periodically experience so-called aregenerator (aplastic) crises, characterized by severe bone marrow failure with predominant damage to the erythroid germ. In an aregenerator crisis, a sharp decrease in the number of reticulocytes is observed, up to their complete disappearance from the peripheral blood. Anemia can quickly develop into a severe, life-threatening form, since even partial compensation of the process is impossible due to the reduced lifespan of erythrocytes. Crises are potentially dangerous, life-threatening complications in any hemolytic process.

Hemolysis is the diffusion of hemoglobin from erythrocytes. When "old" erythrocytes are destroyed in the spleen, liver, and bone marrow, hemoglobin is released, which binds to the plasma proteins haptoglobin, hemopexin, and albumin. These complex compounds are subsequently captured by hepatocytes. Haptoglobin is synthesized in the liver and belongs to the class of alpha ₂ -globulins. During hemolysis, a hemoglobin-haptoglobin complex is formed, which does not penetrate the glomerular barrier of the kidneys, which provides protection against damage to the renal tubules and against iron loss. Hemoglobin-haptoglobin complexes are removed from the vascular bed by cells of the reticuloendothelial system. Haptoglobin is a valuable indicator of the hemolytic process; in severe hemolysis, haptoglobin consumption exceeds the liver's ability to synthesize it, due to which its level in the serum is significantly reduced.

Bilirubin is a product of heme catabolism. Under the influence of heme oxygenase, contained in macrophages of the spleen, liver, bone marrow, the α-methine bridge of the tetrapyrrole nucleus is broken in heme, which leads to the formation of verdogemoglobin. At the next stage, iron is split off, and biliverdin is formed. Under the influence of cytoplasmic biliverdin reductase, biliverdin is converted into bilirubin. Free (unconjugated) bilirubin released from macrophages, when entering the bloodstream, binds to albumin, which delivers bilirubin to hepatocytes. In the liver, albumin is separated from bilirubin, then in the hepatocyte, unconjugated bilirubin binds to glucuronic acid, and monoglucuronide of bilirubin (MGB) is formed. MGB is excreted into bile, where it is converted into bilirubin diglucuronide (DBG). DBG is excreted from bile into the intestine, where it is reduced to the colorless pigment urobilinogen under the influence of microflora, and then to pigmented stercobilin. During hemolysis, the content of free (unconjugated, indirect) bilirubin in the blood increases sharply. Hemolysis promotes increased excretion of heme pigments into bile. As early as the 4th year of life, pigment stones consisting of calcium bilirubinate may form in a child. In all cases of pigment cholelithiasis in children, it is necessary to exclude the possibility of a chronic hemolytic process.

If the amount of free hemoglobin in the plasma exceeds the reserve hemoglobin-binding capacity of haptoglobin, and the flow of hemoglobin from hemolyzed erythrocytes in the vascular bed continues, hemoglobinuria occurs. The appearance of hemoglobin in the urine gives it a dark color (the color of dark beer or a strong solution of potassium permanganate). This is due to the content of both hemoglobin and methemoglobin formed during urine standing, as well as hemoglobin breakdown products - hemosiderin and urobilin.

Depending on the localization, it is customary to distinguish intracellular and intravascular hemolysis variants. In intracellular hemolysis, the destruction of erythrocytes occurs in the cells of the reticuloendothelial system, primarily in the spleen, and to a lesser extent in the liver and bone marrow. Clinically, icterus of the skin and sclera, splenomegaly, and hepatomegaly are observed. A significant increase in the level of indirect bilirubin is recorded, and the level of haptoglobin decreases.

In intravascular hemolysis, the destruction of red blood cells occurs directly in the bloodstream. Patients experience fever, chills, and pain of various localizations. Skin and sclera icterus is moderate, and splenomegaly is not typical. The concentration of free hemoglobin in plasma increases sharply (blood serum turns brown when left to stand due to the formation of methemoglobin), the level of haptoglobin decreases significantly to its complete absence, hemoglobinuria occurs, which can cause acute renal failure (obstruction of the renal tubules by detritus), andDIC syndrome may develop. Starting from the 7th day from the onset of the hemolytic crisis, hemosiderin is detected in the urine.

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Pathophysiology of hemolytic anemia

The membrane of senescent red blood cells undergoes gradual destruction, and they are cleared from the bloodstream by phagocytic cells of the spleen, liver, and bone marrow. Destruction of hemoglobin occurs in these cells and hepatocytes via the oxygenation system with the preservation (and subsequent reutilization) of iron, degradation of heme to bilirubin through a series of enzymatic transformations with protein reutilization.

Increased unconjugated (indirect) bilirubin and jaundice occur when the conversion of hemoglobin to bilirubin exceeds the liver's ability to form bilirubin glucuronide and excrete it with bile. Bilirubin catabolism causes increased stercobilin in feces and urobilinogen in urine and sometimes the formation of gallstones.

Hemolytic anemia

Mechanism

Disease

Hemolytic anemias associated with intrinsic red blood cell abnormality

Hereditary hemolytic anemias associated with structural or functional disorders of the red blood cell membrane	Congenital erythropoietic porphyria. Hereditary elliptocytosis. Hereditary spherocytosis
Acquired hemolytic anemias associated with structural or functional disorders of the erythrocyte membrane	Hypophosphatemia. Paroxysmal nocturnal hemoglobinuria. Stomatocytosis
Hemolytic anemias associated with impaired red blood cell metabolism	Embden-Meyerhof Pathway Enzyme Defect. G6PD Deficiency
Anemias associated with impaired globin synthesis	Carriage of stable abnormal Hb (CS-CE). Sickle cell anemia. Thalassemia

Hemolytic anemias associated with external influences

Hyperactivity of the reticuloendothelial system	Hypersplenism
Antibody-related hemolytic anemias	Autoimmune hemolytic anemias: with warm antibodies; with cold antibodies; paroxysmal cold hemoglobinuria
Hemolytic anemias associated with exposure to infectious agents	Plasmodium. Bartonella spp
Hemolytic anemias associated with mechanical trauma	Anemias caused by the destruction of red blood cells when they come into contact with a prosthetic heart valve. Trauma-induced anemia. March hemoglobinuria

Hemolysis occurs primarily extravascularly in the phagocytic cells of the spleen, liver, and bone marrow. The spleen typically contributes to the shortening of red blood cell survival by destroying abnormal red blood cells and those with warm antibodies on their surface. An enlarged spleen can sequester even normal red blood cells. Red blood cells with severe abnormalities and those with cold antibodies or complement (C3) on their membrane surface are destroyed within the bloodstream or in the liver, where the destroyed cells can be effectively removed.

Intravascular hemolysis is rare and results in hemoglobinuria when the amount of hemoglobin released into the plasma exceeds the hemoglobin-binding capacity of proteins (e.g., haptoglobin, which is normally present in plasma at a concentration of about 1.0 g/L). Unbound hemoglobin is reabsorbed by renal tubular cells, where the iron is converted to hemosiderin, part of which is assimilated for reutilization, and part of which is excreted in the urine when the tubular cells are overloaded.

Hemolysis may be acute, chronic, or episodic. Chronic hemolysis may be complicated by aplastic crisis (temporary failure of erythropoiesis), most often as a result of infection, usually caused by parvovirus.

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Symptoms of hemolytic anemia

Hemolytic anemia, regardless of the causes directly causing hemolysis, has 3 periods in its course: the period of hemolytic crisis, the period of subcompensation of hemolysis and the period of compensation of hemolysis (remission). Hemolytic crisis is possible at any age and is most often provoked by an infectious disease, vaccination, cooling or taking medications, but can also occur without apparent reasons. During the crisis period, hemolysis increases sharply and the body is unable to quickly replenish the required number of red blood cells and convert the excess indirect bilirubin into direct. Thus, hemolytic crisis includes bilirubin intoxication and anemic syndrome.

Symptoms of hemolytic anemia, and more specifically bilirubin intoxication syndrome, are characterized by jaundice of the skin and mucous membranes, nausea, vomiting, abdominal pain, dizziness, headaches, fever, and in some cases, impaired consciousness and convulsions. Anemic syndrome is represented by pale skin and mucous membranes, enlarged heart borders, muffled tones, tachycardia, systolic murmur at the apex, shortness of breath, weakness, and dizziness. Intracellular hemolysis is characterized by hepatosplenomegaly, while intravascular or mixed hemolysis is characterized by a change in urine color due to hemoglobinuria.

During a hemolytic crisis, the following complications of hemolytic anemia are possible: acute cardiovascular failure (anemic shock), DIC syndrome, aregenerator crisis, acute renal failure, and "bile thickening" syndrome. The period of subcompensation of hemolysis is also characterized by increased activity of the erythroid germ of the bone marrow and liver, but only to the extent that does not lead to compensation of the main syndromes. In this regard, the patient may retain moderate clinical symptoms: pallor, subicteric skin and mucous membranes, slight (or pronounced depending on the form of the disease) enlargement of the liver and / or spleen. Fluctuations in the number of erythrocytes from the lower limit of the norm to 3.5-3.2 x 10 ¹² /l and, accordingly, hemoglobin within 120-90 g / l, as well as indirect hyperbilirubinemia up to 25-40 μmol / l are possible. During the period of hemolysis compensation, the intensity of erythrocyte destruction is significantly reduced, the anemic syndrome is completely stopped due to hyperproduction of erythrocytes in the erythroid sprout of the bone marrow, while the content of reticulocytes is always increased. At the same time, the active work of the liver to convert indirect bilirubin into direct ensures a decrease in the bilirubin level to normal.

Thus, both main pathogenetic mechanisms that determine the severity of the patient's condition during a hemolytic crisis are stopped in the compensation period due to increased bone marrow and liver function. At this time, the child does not have clinical manifestations of hemolytic anemia. During the hemolysis compensation period, complications such as hemosiderosis of internal organs, biliary dyskinesia, and spleen pathology (infarctions, subcapsular ruptures, hypersplenism syndrome) are also possible.

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Structure of hemolytic anemias

Currently, it is generally accepted to distinguish between hereditary and acquired forms of hemolytic anemia.

Among hereditary hemolytic anemias, depending on the nature of the erythrocyte damage, there are forms associated with a violation of the erythrocyte membrane (impaired membrane protein structure or impaired membrane lipids); forms associated with impaired activity of erythrocyte enzymes (pentose phosphate cycle, glycolysis, glutathione metabolism, etc.) and forms associated with impaired structure or synthesis of hemoglobin. In hereditary hemolytic anemias, a reduction in the lifespan of erythrocytes and premature hemolysis are genetically determined: there are 16 syndromes with a dominant type of inheritance, 29 with a recessive type and 7 hereditary phenotypes linked to the X chromosome. Hereditary forms predominate in the structure of hemolytic anemias.

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Acquired hemolytic anemias

In acquired hemolytic anemias, the lifespan of red blood cells decreases under the influence of various factors, so they are classified according to the principle of specifying the factors causing hemolysis. These are anemias associated with the influence of antibodies (immune), with mechanical or chemical damage to the red blood cell membrane, destruction of red blood cells by a parasite ( malaria ), vitamin deficiency (vitamin E deficiency), with a change in the structure of membranes caused by somatic mutation ( paroxysmal nocturnal hemoglobinuria ).

In addition to the above signs common to all hemolytic anemias, there are symptoms pathognomonic for a specific form of the disease. Each hereditary form of hemolytic anemia has its own differential diagnostic signs. Differential diagnosis between different forms of hemolytic anemia should be carried out in children over one year of age, since at this time the anatomical and physiological features characteristic of the blood of young children disappear: physiological macrocytosis, fluctuations in the number of reticulocytes, predominance of fetal hemoglobin, a relatively low limit of the minimum osmotic stability of erythrocytes.

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Hereditary hemolytic anemias

Hereditary hemolytic anemias associated with a disorder of the red blood cell membrane (membranopathies)

Membranopathies are characterized by a hereditary defect in the structure of membrane proteins or a disorder of the lipids of the erythrocyte membrane. They are inherited in an autosomal dominant or augosomal recessive manner.

Hemolysis is usually localized intracellularly, that is, the destruction of red blood cells occurs mainly in the spleen, and to a lesser extent in the liver.

Classification of hemolytic anemias associated with damage to the red blood cell membrane:

1. Disruption of the structure of the erythrocyte membrane protein
   1. hereditary microspherocytosis;
   2. hereditary elliptocytosis;
   3. hereditary stomatocytosis;
   4. hereditary pyropoikilocytosis.
2. Disruption of erythrocyte membrane lipids
   1. hereditary acanthocytosis;
   2. hereditary hemolytic anemia due to deficiency of lecithin-cholesterol acyltransferase activity;
   3. hereditary nonspherocytic hemolytic anemia caused by an increase in phosphatidylcholine (lecithin) in the erythrocyte membrane;
   4. infantile pycnocytosis.

Disruption of the structure of the erythrocyte membrane protein

Rare forms of hereditary anemia caused by a disorder in the structure of red blood cell membrane proteins

Hemolysis in these forms of anemia occurs intracellularly. Hemolytic anemia has varying degrees of severity - from mild to severe, requiring blood transfusions. Paleness of the skin and mucous membranes, jaundice, splenomegaly, and possible development of cholelithiasis are noted.

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Diagnosis of hemolytic anemia

Hemolysis is suspected in patients with anemia and reticulocytosis, especially in the presence of splenomegaly, as well as other possible causes of hemolysis. If hemolysis is suspected, a peripheral blood smear is examined, serum bilirubin, LDH, and ALT are determined. If these studies do not give results, hemosiderin, urinary hemoglobin, and serum haptoglobin are determined.

In hemolysis, one can assume the presence of morphological changes in red blood cells. The most typical for active hemolysis is erythrocyte spherocytosis. Red blood cell fragments (schistocytes) or erythrophagocytosis in blood smears suggest the presence of intravascular hemolysis. In spherocytosis, there is an increase in the MCHC index. The presence of hemolysis can be suspected by an increase in the levels of serum LDH and indirect bilirubin with a normal ALT value and the presence of urinary urobilinogen. Intravascular hemolysis is assumed by detecting a low level of serum haptoglobin, but this indicator can be reduced in liver dysfunction and increased in the presence of systemic inflammation. Intravascular hemolysis is also assumed by detecting hemosiderin or hemoglobin in the urine. The presence of hemoglobin in the urine, as well as hematuria and myoglobinuria, is determined by a positive benzidine test. Differential diagnostics of hemolysis and hematuria is possible based on the absence of red blood cells during urine microscopy. Free hemoglobin, unlike myoglobin, can stain plasma brown, which is evident after blood centrifugation.

Morphological changes in erythrocytes in hemolytic anemia

Morphology	Reasons
Spherocytes	Transfused red blood cells, warm antibody hemolytic anemia, hereditary spherocytosis
Schistocytes	Microangiopathy, intravascular prosthetics
Target-shaped	Hemoglobinopathies (Hb S, C, thalassemia), liver pathology
Sickle-shaped	Sickle cell anemia
Agglutinated cells	Cold agglutinin disease
Heinz bodies	Activation of peroxidation, unstable Hb (eg, G6PD deficiency)
Nucleated red blood cells and basophilia	Beta thalassemia major
Acanthocytes	Spurred cell anemia

Although the presence of hemolysis can be determined by these simple tests, the decisive criterion is the determination of the life span of the red blood cells by testing with a radioactive tracer such as ⁵¹ Cr. Determining the life span of the labeled red blood cells can reveal the presence of hemolysis and the location of their destruction. However, this test is rarely used.

When hemolysis is detected, it is necessary to establish the disease that provoked it. One way to limit the differential search for hemolytic anemia is to analyze the patient's risk factors (e.g., geographic location of the country, heredity, existing diseases), identify splenomegaly, determine the direct antiglobulin test (Coombs), and study the blood smear. Most hemolytic anemias have deviations in one of these variants, which can direct further search. Other laboratory tests that can help in determining the cause of hemolysis are quantitative hemoglobin electrophoresis, erythrocyte enzyme testing, flow cytometry, determination of cold agglutinins, erythrocyte osmotic resistance, acid hemolysis, glucose test.

Although certain tests can help differentiate intravascular from extravascular hemolysis, making these distinctions can be difficult. During intense red blood cell destruction, both mechanisms occur, although to varying degrees.

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Treatment of hemolytic anemia

Treatment of hemolytic anemia depends on the specific mechanism of hemolysis. Hemoglobinuria and hemosiderinuria may require iron replacement therapy. Long-term transfusion therapy results in extensive iron deposition, requiring chelation therapy. Splenectomy may be effective in some cases, especially when splenic sequestration is the primary cause of red blood cell destruction. Splenectomy should be delayed for 2 weeks after administration of pneumococcal, meningococcal, and Haemophilus influenzae vaccines, if possible.

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