Hemolytic disease of the newborn

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Overview
Haemolytic disease of the newborn, also known as HDN or Erythroblastosis fetalis, is an alloimmune condition that develops in a fetus, when the IgG antibodies that have been produced by the mother and have passed through the placenta include ones which attack the red blood cells in the fetal circulation. The red cells are broken down and the fetus can develop reticulocytosis and anaemia. This fetal disease ranges from mild to very severe, and fetal death from heart failure (hydrops fetalis) can occur. When the disease is moderate or severe, many erythroblasts are present in the foetal blood and so these forms of the disease can be called erythroblastosis fetalis (or erythroblastosis foetalis).

Symptoms
Hemolysis leads to elevated bilirubin levels. After delivery bilirubin is no longer cleared (via the placenta) from the neonate's blood and the symptoms of jaundice (yellowish skin and yellow discolouration of the whites of the eyes) increase within 24 hours after birth. Like any other severe neonatal jaundice, there is the possibility of acute or chronic kernicterus.

Profound anemia can cause high-output heart failure, with pallor, enlarged liver and/or spleen, generalized swelling, and respiratory distress. The prenatal manifestations are known as hydrops fetalis; in severe forms this can include petechiae and purpura. The infant may be stillborn or die shortly after birth.

Causes
Antibodies are produced when the body is exposed to an antigen foreign to the make-up of the body. If a mother is exposed to an alien antigen and produces IgG (as opposed to IgM which does not cross the placenta), the IgG will target the antigen, if present in the fetus, and may affect it in utero and persist after delivery. The three most common models in which a woman becomes sensitized toward (i.e., produces IgG antibodies against) a particular blood type are:


 * Fetal-maternal hemorrhage can occur due to trauma, abortion, childbirth, ruptures in the placenta during pregnancy, or medical procedures carried out during pregnancy that breach the uterine wall. In subsequent pregnancies, if there is a similar incompatibility in the fetus, these antibodies are then able to cross the placenta into the fetal bloodstream to attach to the red blood cells and cause hemolysis. In other words, if a mother has anti-RhD (D being the major Rhesus antigen) IgG antibodies as a result of previously carrying a RhD-positive fetus, this antibody will only affect a fetus with RhD-positive blood.


 * The woman may receive a therapeutic blood transfusion with an incompatible blood type. ABO blood group system and Rhesus blood group system typing are routine prior to transfusion.  Suggestions have been made that women of child bearing age or young girls should not be given a transfusion with Rhc-positive blood or Kell1-positive blood to avoid possible sensitization, but this would strain the resources of blood transfusion services, and it is currently considered uneconomical to screen for these blood groups.


 * The third sensitization model can occur in women of blood type O. The immune response to A and B antigens, that are widespread in the environment, usually leads to the production of IgM anti-A and IgM anti-B antibodies early in life. On rare occasions, IgG antibodies are produced.  In contrast, Rhesus antibodies are generally not produced from exposure to environmental antigens.

Serological diagnoses

 * ABO system
 * ABO hemolytic disease of the newborn can range from mild to severe, but generally it is a mild disease.
 * anti-A antibodies
 * anti-B antibodies


 * Rhesus system (the Rh d antigen and Rh d antibodies do not exist)
 * rhesus D hemolytic disease of the newborn (often called Rh disease) is the most common form of severe HDN. The disease varies from mild to severe.
 * rhesus E hemolytic disease of the newborn is a mild condition
 * rhesus c hemolytic disease of the newborn can range from a mild to severe disease - is the third most common form of severe HDN
 * rhesus e hemolytic disease of the newborn - rare
 * rhesus C hemolytic disease of the newborn - rare
 * antibody combinations (ie anti-Rhc and anti-RhE antibodies occurring together) - can be severe


 * Kell system
 * anti-Kell hemolytic disease of the newborn
 * anti-K1 antibodies - disease ranges from mild to severe - over half of the cases are caused by multiple blood transfusions - is the second most common form of severe HDN
 * anti-K2 ,anti-K3 and anti-K4 antibodies - rare


 * Other blood group antibodies (Kidd, Lewis, Duffy, MN, P and others).

Diagnosis
The diagnosis of HDN is based on history and laboratory findings:

Blood tests done on the newborn baby
 * Biochemistry tests for jaundice
 * Peripheral blood morphology shows increased reticulocytes. Erythroblasts (also known as nucleated red blood cells) occur in moderate and severe disease.

Blood tests done on the mother
 * Positive direct Coombs test (might be negative after fetal interuterine blood transfusion)
 * Positive indirect Coombs test

Treatment
Before birth, options for treatment include intrauterine transfusion or early induction of labor when pulmonary maturity has been attained, fetal distress is present, or 35 to 37 weeks of gestation have passed. The mother may also undergo plasma exchange to reduce the circulating levels of antibody by as much as 75%. After birth, treatment depends on the severity of the condition, but could include temperature stabilization and monitoring, phototherapy, transfusion with compatible packed red blood, exchange transfusion with a blood type compatible with both the infant and the mother, sodium bicarbonate for correction of acidosis and/or assisted ventilation. Rhesus-negative mothers who have had a pregnancy with/are pregnant with a rhesus-positive infant are given Rh immune globulin (RhIG) at 28 weeks during pregnancy and within 72 hours after delivery to prevent sensitization to the D antigen. It works by binding any fetal red cells with the D antigen before the mother is able to produce an immune response and form anti-D IgG. A drawback to pre-partum administration of RhIG is that it causes a positive antibody screen when the mother is tested which is indistinguishable from immune reasons for antibody production.

Complications
Complications of HDN could include kernicterus, hepatosplenomegaly, inspissated (thickened or dried) bile syndrome and/or greenish staining of the teeth, hemolytic anemia and damage to the liver due to excess bilirubin.

Similar conditions
Similar conditions include acquired hemolytic anemia, congenital toxoplasma and syphilis infection, congenital obstruction of the bile duct and cytomegalovirus infection.