Hemolytic Disease of  Newborn (HDN)

What sample is needed for the Hemolytic Disease of the Newborn (HDN) workup?

1. The sample is serum from the mother.
2. Whole blood (RBC) from the fetus or newborn.

What are the indications for the Coombs’ test?

1. To diagnose hemolytic anemia of the newborn (hemolytic disease of the newborn = HDN).
2. To find out the presence of an anti-D antibody in the mother’s serum.

How will you define hemolytic disease of newborns (HDN)?

1. HDN is an immune-mediated hemolysis of fetal RBCs caused by the transfer of the maternal IgG antibodies directed against fetal RBC antigens.
2. In HDN, the mother is always Rh-negative. Fetus inherit Rh-Positve RBC from the father.
3. Hemolytic disease of the newborn (HDN) results from maternal alloantibodies that cross the placenta and enter fetal circulation, causing hemolysis.
4. IgG antibodies pass from the mother’s placenta to the fetus, where they bind to fetal RBCs and destroy them.
   1. Anti-D antibodies are responsible for most cases of severe HDN.
5. This condition is also called erythroblastosis fetalis.
6. ABO incompatibility is more common but is less severe.

How will you discuss the pathophysiology of hemolytic anemia of the newborn (HDN)?

1. Red blood cells have various antigens on their surface, which form blood groups. The Blood group ABO system and the Rh system (D-antigen) are important.
2. Hemolytic disease of the newborn (HDN) results when fetal antigens are present on RBCs, and the mother’s RBCs lack the Rh antigen.
3. Fetal antigens provoke the formation of maternal IgG antibodies. It happens when the fetal RBCs enter the maternal circulation during delivery (or pregnancy).
4. These maternal antibodies (IgG) can cross the placenta and enter fetal circulation, leading to hemolytic anemia by attacking the fetal RBCs.
5. If the mother and fetus are ABO-incompatible, sensitization cannot occur because maternal AB antibodies immediately destroy fetal RBCs.
6. A Rh-positive baby occurs in ∼10% of Rh-negative mothers in white females, 5% in black females, and 1% in Asian females.

What is the outcome of Rh-incompatibility?

1. Hemolytic disease of the newborn due to Rh-incompatibility varies in severity:
   1. Subclinical disease.
   2. Mild jaundice with anemia.
   3. Erythroblastosis fetalis is a dangerous condition.
   4. The main findings are jaundice and anemia.
   5. Reticulocytosis >6% accompanies the anemia.
   6. In severe cases, nucleated RBCs are present on the peripheral blood smear.
2. Jaundice is due mainly to unconjugated (indirect) bilirubin.
   1. Jaundice is not present at birth; it appears after 24 hours.
   2. Physiologic jaundice may be confused with pathological jaundice. Physiologic jaundice has no anemia.
   3. Normal hemoglobin in newborns is 18 g/dL; anemia is established when hemoglobin is <15 g/dL.
3. Direct Coombs’ test is positive.

How will you discuss the Rh system?

1. If the Rh-antigen is present in some of the RBCs, those are called Rh-positive blood groups, while the RBCs lack Rh – antigens and are called Rh-negative blood groups.
   1. The other common causes are the Rh-c antigen and the blood group Kell antigens.
2. There is a group of Rh antigens, such as Rh-C, Rh-D, Rh-E, and others.
3. Suppose the mother is Rh-antigen (D-negative) and the baby is Rh-antigen (D-positive) because of the feto-maternal hemorrhage. In that case, the mother may be sensitized to the Rh-antigen and develop Rh antibodies, mostly IgG-type (anti-D) antibodies.

What is the mechanism of Rh-incompatibility?

1. This sensitization occurs due to pregnancy, abortion, ectopic pregnancy, placental trauma, amniocentesis, blood transfusion with Rh-positive RBCs, or contaminated blood products like platelet concentrates.
2. The most common is the fetomaternal mixing of Rh-positive fetal RBCs.
3. This mixing occurs after 16 weeks of pregnancy or a single large dose of fetal RBCs at the time of delivery.
4. 10% to 13% of mothers risk sensitization by the Rh-positive fetal RBCs.
5. Usually, the first child is not affected.
6. Firstborn infants are affected by 5% to 10% with HDN, either due to a previous pregnancy or abortion, or the high sensitivity of the mother to Rh-antigens.

7. Usually, the mother and fetus are ABO compatible.
8. These maternal anti-D antibodies can cross the placental barrier, enter the fetal circulation, and cause hemolytic disease of the newborn (HDN).

How will you diagnose Hemolytic anemia in a newborn (HDN)?

1. In the case of Rh-induced hemolytic anemia of the newborn (HDN), the direct Coombs test on cord blood is positive.
2. The Coombs test is frequently, but not always, positive in ABO-induced HDN in cord blood.
3. The direct Coombs test on infant blood is usually positive in Rh-induced HDN but negative in ABO-induced HDN when done more than 24 hours after delivery.
4. Cord blood bilirubin usually increases, and cord blood hemoglobin is decreased in severe HDN.

What is the significance of the Coombs’ test for hemolytic disease of newborns (HDN)?

1. Coombs’ test is used to detect antibodies in Rh-negative mothers or newborns.
   1. Mother has free antibodies in the serum.
   2. The fetus/newborn has coated RBCs with antibodies.
2. One can monitor the presence of the antibody during pregnancy.
   1. A maternal titer of more than 1:16 at the 8th month indicates the presence of anti-D antibodies in the mother. These can cross the placental barrier and enter fetal circulation.
   2. The fetus can develop hemolytic disease.

How will you discuss an indirect Coombs’ test?

• It is performed to detect a free anti-D antibody in maternal serum.

How will you discuss A direct Coomb’s test?

• The Coombs test is done to find RBC-coated antibodies in the fetus or newborn.

How will you do Prenatal screening?

1. Must do blood group ABO and Rh at the first prenatal visit during the pregnancy.
2. Advise an indirect Coombs’ test for the mother to check for ABO or other antigens.
3. Rh-negative mothers should be given anti-D immunoglobulin (Rhogam) at the end of the second trimester and again within 72 hours of delivery in the case of Rh-positive babies. This treatment will decrease the prevalence of HDN.
4. Monitor the anti-D titer in the mother’s serum to detect sensitization when the titer is >1:8.
   1. If the titer is ≥1:32, advise serial estimation of the amniotic fluid bilirubin (indirect) level every 2 to 3 weeks to prevent the risk to the fetus.
5. Lecithin-to-sphingomyelin ratio estimation provides an indication of lung maturity.
6. Amniocentesis is more reliable than the anti-D titer in determining the severity of the HDN.
7. DNA analysis of amniotic fluid by PCR can determine the D-antigen status of the fetus.
8. At birth, determine the cord blood (baby’s blood):
   1. Hemoglobin.
   2. Bilirubin level.
   3. Direct Coombs’ test.

How will you do the postnatal workup and follow-up?

1. Check the infant’s indirect serum bilirubin, as it rises rapidly. There may be an increase of 0.3-1.0 mg/dL/hour. It may reach 30 mg/dL in untreated babies in 3 to 5 days; at this level, the baby may die.
2. Urobilinogen is increased in urine and feces. This increase will be parallel to blood serum bilirubin.
3. The direct Coombs’ test is positive on cord blood RBCs for Rh, Kell, Kidd, and Duffy antibodies.
4. It is weakly positive in anti-A antibodies.
5. Anemia is not evident at birth but becomes maximum by the 3rd or 4th day.
6. Blood examination of the baby will show:
   1. MCHC is normal, and MCV and MCH are increased.
   2. Peripheral blood smears show increased nucleated RBCs in the first 2 days. Their number will decrease, and they may be absent on the 3rd or 4th day.
   3. It shows anisocytosis, polychromatophilia, and increased macrocytes.
   4. There is reticulocytosis >6% and sometimes may reach 30% to 40%.
   5. WBC count is increased.
   6. The platelet count is mostly normal.
7. When these babies are treated, this episode will resolve in 3 to 6 weeks, and there will be no further maternal antibodies.

What is the prognosis of Hemolytic Disease of the Newborn (HDN)?

• Its (HDN) prevalence is markedly decreased due to the in-time administration of Rhogam after abortion or delivery.

How will you treat hemolytic disease in a newborn (HDN)?

1. The exchange of blood transfusion can save infants with HDN.
2. Indications/criteria for blood exchange transfusion:
   1. Infants’ serum bilirubin level >20 mg/dL or in premature or severely ill infants with a bilirubin level of 15 mg/dL.
   2. Cord blood indirect bilirubin level >3 mg/dL.
   3. Cord blood hemoglobin is <13 g/dL, and there are references in favor of 8 to 14 g/dL.
   4. Maternal Rh-antibody titer of 1:64 or greater. If bilirubin does not rise, then this is not the indication.

What are the criteria for the blood exchange transfusion?

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