7.3 Hemolytic Disease of the Newborn

7.3 Hemolytic Disease of the Newborn

Quick Answer: Rh incompatibility is usually anti-D IgG from an Rh-negative mother against an Rh-positive infant, often after prior sensitization, and can cause hydrops, severe anemia, and dangerous bilirubin. ABO incompatibility is typically a group O mother and a group A or B infant and often occurs in a first pregnancy. A positive Direct Antiglobulin Test (DAT) supports antibody on infant red cells. Treat immune hemolysis with intensive phototherapy, IVIG, and exchange transfusion when needed. Teach hemolysis here; the full hour-specific bilirubin nomogram belongs in Chapter 13.

Hemolytic disease of the newborn (HDN, erythroblastosis fetalis in older language) is the third Hematology/Immunology leaf of the 20% Endocrine, Hematology/Immunology, GI, Renal/GU, and Integumentary domain. Hyperbilirubinemia is also a Multisystem problem (MU-8). This section owns why the cells break and the immune-specific therapies. Chapter 13 owns the phototherapy and exchange nomograms, hour-of-life plotting, and the broader jaundice differential (breast-milk jaundice, dehydration, biliary atresia). OpenExamPrep independent study material covers HDN as listed on AACN Certification Corporation's current Neonatal CCRN Test Plan.

IgG crosses the placenta. IgM does not. That single sentence explains why naturally occurring IgM anti-A and anti-B do not wreck every type-A fetus of a type-O mother, and why the IgG subset of anti-A/B—and why anti-D after sensitization—can. Coated red cells are removed by Fc-receptor-bearing macrophages in spleen and liver. Hemoglobin falls. Indirect bilirubin rises. The marrow throws out nucleated red cells. In the worst fetal cases, high-output failure and hypoalbuminemia produce hydrops.

Rh incompatibility (anti-D)

An RhD-negative mother can form anti-D after exposure to RhD-positive red cells: a prior pregnancy, miscarriage, abruption, invasive procedure, or transfusion. Rh immunoglobulin (RhIg) given during pregnancy and after delivery of an Rh-positive infant (and after sensitizing events) prevents most anti-D formation. It does nothing useful if the mother is already immunized. Typical U.S. teaching includes a dose around 28 weeks and another after birth if the infant is Rh-positive; exact products and windows follow obstetric protocol, not an AACN milligram table.

In a subsequent (or already-sensitized) pregnancy, anti-D IgG crosses, coats fetal Rh-positive cells, and macrophages destroy them. Fetal anemia can reach hydrops: high-output heart failure, hypoalbuminemia, pleural and pericardial effusions, ascites, and anasarca. Hydrops is also taught as a Multisystem problem (Chapter 15); here the mechanism is immune hemolytic anemia. Nucleated red cells flood the circulation (erythroblastosis). After birth the infant may be pale, jaundiced (sometimes delayed a few hours until extra bilirubin hits a still-maturing liver), hepatosplenomegalic, and DAT-positive. Bilirubin can rise fast enough to threaten the brain (acute bilirubin encephalopathy, and with chronic injury kernicterus).

Intrauterine transfusion is a fetal-therapy answer for severe anemia before birth. After birth: support airway and circulation, correct anemia with PRBCs (often irradiated, CMV-safe, compatible with maternal antibody—typically O-negative red cells that lack the offending antigen), intensive phototherapy, IVIG, and exchange transfusion if bilirubin or anemia remains dangerous despite those steps.

Other Rh and non-Rh antibodies (anti-c, anti-Kell, anti-E, and others) produce a similar picture. Anti-Kell can suppress marrow as well as hemolyze. You do not need every eponym; you need maternal IgG alloantibody plus an antigen-positive infant plus hemolysis.

ABO incompatibility

Mother group O, infant group A or B is the classic pairing. Group O adults make IgG (as well as IgM) anti-A and anti-B. Those IgG antibodies can cross in a first pregnancy—unlike typical anti-D, which usually needs a priming exposure. ABO HDN is usually milder than anti-D disease. Hydrops is uncommon. Jaundice in the first 24 hours, a modest anemia, spherocytes on the smear, and a positive or weakly positive DAT are typical. Neonatal A and B antigen density is lower than in adults, which is one reason the disease is milder and the DAT can be weakly positive.

Do not ignore ABO disease because it is usually mild. A rapidly rising bilirubin still needs intensive phototherapy and may still need IVIG or exchange. Do not diagnose ABO HDN when the mother is A and the infant is O; that pairing does not produce this antibody story. Do not tell families that a first baby is automatically safe from immune hemolysis; that myth belongs to anti-D, not to ABO.

Direct Antiglobulin Test and the laboratory picture

The Direct Antiglobulin Test (DAT, direct Coombs) detects antibody or complement already bound to the infant's red cells. A positive DAT in this setting supports immune hemolysis. Send blood type, DAT, hemoglobin, bilirubin (total and direct), reticulocyte count, and a smear. The indirect antiglobulin test looks for antibody in serum; maternal antibody screens tell you which alloantibody is in play. Cord blood type and DAT are often collected when the mother is group O or Rh-negative or has a known alloantibody.

A negative DAT does not exclude all hemolysis. G6PD deficiency, hereditary spherocytosis, enclosed hemorrhage (cephalohematoma, subgaleal), and sepsis can raise bilirubin without coating cells with maternal IgG. Those belong on the jaundice list in Chapter 13. A positive DAT with no jaundice and a stable hemoglobin still needs surveillance, because hemolysis can declare over hours. Rising reticulocytes, falling hemoglobin, and a rising unconjugated bilirubin are the kinetic signature that phototherapy is not optional.

Typical quiet respiratory rates remain about 40-60 breaths/min in an unassisted term infant. A hydropic, anemic infant may be tachypneic because of pulmonary edema, pleural fluid, or high-output failure—not because TTN is the main diagnosis. Heart rates of 180-200 in a pale, DAT-positive neonate are high-output physiology until you have given compatible red cells.

Phototherapy, IVIG, and exchange: principles here, nomogram in Chapter 13

Phototherapy converts bilirubin to water-soluble isomers that can be excreted without conjugation. Use intensive phototherapy: appropriate irradiance, adequate skin exposure, eye protection, temperature control near 36.5-37.5 °C, hydration, and ongoing bilirubin checks. Thresholds are hour-of-life and gestational-age specific. AACN does not print a phototherapy number on the test plan. The AAP hour-specific nomogram and the full discussion of rebound, conjugated versus unconjugated bilirubin, and breast-milk jaundice live in Chapter 13. For HDN, remember that hemolysis can outrun standard phototherapy; these infants often qualify for treatment earlier than a well term infant with no risk flags. Plot the bilirubin. Do not memorize a single milligram-per-deciliter cutoff as if it were an AACN constant.

IVIG (often discussed in protocols near 0.5-1 g/kg) occupies Fc receptors on macrophages and can slow immune hemolysis, reducing the need for exchange in isoimmune disease. Follow the unit protocol. IVIG is not a bilirubin sponge and it does not replace phototherapy. Watch for fluid overload and rare hemolytic or inflammatory reactions.

Double-volume exchange transfusion removes antibody-coated cells and bilirubin and replaces them with antigen-negative blood. Indications are protocolized: bilirubin at or above the exchange line despite intensive phototherapy, signs of acute bilirubin encephalopathy, or severe anemia in HDN. A conceptual double-volume exchange uses about 160 mL/kg in term infants (two times an estimated 80 mL/kg blood volume); preterm blood volume estimates are higher per kilogram—follow the unit calculator. Complications include thrombosis, electrolyte shifts (hypocalcemia from citrate), thrombocytopenia, infection, arrhythmia, and necrotizing enterocolitis. Nursing owns access (often UVC), thermoregulation, calcium monitoring, slow accounted aliquots, and a second checker on volumes.

Hydrops from anemia needs airway support, cautious drainage of effusions when they impair ventilation, and red-cell transfusion—sometimes a small partial exchange if volume overload is extreme—rather than a casual 20 mL/kg bolus into a failing heart. Full hydrops staging is Chapter 15; the heme action is to treat the anemia and the antibody.

Worked examples and traps

Example A. Rh-negative mother with known anti-D; Rh-positive infant, hydropic, hemoglobin 6 g/dL, DAT strongly positive. After airway and circulatory support, this is severe Rh HDN: antigen-negative PRBCs, intensive phototherapy, IVIG per protocol, and exchange if bilirubin or anemia remains in the danger zone.

Example B. First pregnancy, mother group O, infant group A, jaundice at 18 hours, hemoglobin 13 g/dL, DAT weakly positive, spherocytes. This is ABO HDN. Start intensive phototherapy, plot bilirubin on the unit nomogram (Chapter 13 skill), and discard the second-child-only myth.

Example C. Mother group A, infant group O, DAT negative, jaundice at 60 hours in a well breastfed term infant. This is not ABO HDN. Use Chapter 13 pathways (physiologic jaundice, breast-milk jaundice, dehydration, G6PD, and enclosed hemorrhage).

Traps: exchanging every ABO-incompatible cord blood; ignoring first-day jaundice because ABO is mild; using saline partial exchange (a polycythemia tool from section 7.1) as if it treated antibody-mediated hemolysis; dumping the entire AAP nomogram into this section and skipping hemolysis; calling this OpenExamPrep chapter official AACN procedure training. It is independent teaching covering listed patient problems. Mixed items are at /practice/ccrn-neonatal. Pediatric hemolysis pages at /study-guides/ccrn-pediatric address older children, not this perinatal antibody story.