Hemolytic disease of the newborn

Background

• Hemolytic disease of the fetus and newborn (HDFN), also known as erythroblastosis fetalis, is a condition in which maternal alloantibodies cross the placenta and destroy fetal/neonatal red blood cells, causing hemolytic anemia and unconjugated hyperbilirubinemia. The spectrum ranges from mild self-limited jaundice (most ABO cases) to fatal hydrops fetalis (severe Rh disease).
• The emergency physician encounters HDFN as early-onset neonatal jaundice (within the first 24 hours — always pathologic), severe anemia in a neonate, or a readmission for rapidly rising bilirubin.
• Timely recognition is critical because untreated severe hyperbilirubinemia causes kernicterus.
• ABO incompatibility is now the most common cause of HDFN in the Western world, following the success of anti-D (RhoGAM) prophylaxis in preventing Rh disease
• Rh (D) incompatibility remains the most severe form but is now uncommon with appropriate prevention
• Other minor blood group antigens (Kell, Duffy, Kidd, MNS) cause approximately 10% of severe cases; anti-Kell deserves special attention

Feature	ABO incompatibility	Rh (D) incompatibility	Anti-Kell
Frequency	Most common cause of HDFN	Now uncommon (with prophylaxis)	~10% of severe cases
First pregnancy affected?	Yes (preexisting natural anti-A/B IgG)	Usually no (sensitization during first pregnancy; affects subsequent)	Yes (if prior transfusion) or subsequent pregnancies
Typical severity	Mild to moderate	Moderate to severe	Severe
Direct Coombs (DAT)	Weakly positive or negative	Strongly positive	Positive
Anemia severity	Usually mild	Can be severe → hydrops	Severe (suppresses erythropoiesis directly; anemia out of proportion to hemolysis)
Hydrops fetalis	Rare	Can occur	Can occur
Bilirubin rise	Moderate	Rapid and severe	May be less than expected despite severe anemia (suppressed RBC production)
Prevention	None available	Anti-D immunoglobulin (RhoGAM)	Avoid Kell-positive transfusions in women of childbearing age

Mechanism

• Mother lacks an antigen present on fetal RBCs (inherited from father)
• Maternal immune system produces IgG antibodies against the fetal antigen
• IgG crosses the placenta → binds fetal RBCs → extravascular hemolysis (in fetal spleen/liver)
• Hemolysis → anemia + increased unconjugated bilirubin production
• In utero: bilirubin is cleared by the placenta, so the fetus is not jaundiced; however, severe anemia → high-output cardiac failure → hydrops fetalis
• After birth: the neonatal liver cannot conjugate the sudden bilirubin load → unconjugated hyperbilirubinemia → risk of kernicterus

Clinical features

Early-onset jaundice (the cardinal sign)

• Jaundice within the first 24 hours of life is ALWAYS pathologic and HDFN must be considered
• This distinguishes HDFN from physiologic jaundice (which appears after 24-48 hours)
• Bilirubin may rise rapidly: rate of rise >0.5 mg/dL/hour suggests significant hemolysis and warrants urgent intervention

Spectrum of severity

• Mild: jaundice only; no significant anemia; responds to phototherapy (most ABO cases)
• Moderate: significant jaundice + anemia; may require IVIG and/or exchange transfusion
• Severe: profound anemia, hepatosplenomegaly (from extramedullary hematopoiesis), edema, ascites → hydrops fetalis
• Fatal: stillbirth or neonatal death from severe anemia, heart failure, or kernicterus

Examination findings

• Jaundice (scleral icterus, yellow skin)
• Pallor (anemia — may mask cyanosis)
• Hepatosplenomegaly (extramedullary hematopoiesis; Rh disease more than ABO)
• Edema, ascites, pleural effusions (hydrops — severe cases)
• Petechiae (thrombocytopenia from marrow replacement or DIC)
• Lethargy, poor feeding, hypotonia (early bilirubin encephalopathy — see Kernicterus)

Late anemia (readmission risk)

• Neonates treated for HDFN may develop late anemia at 2-8 weeks of age as maternal antibodies continue to hemolyze neonatal RBCs
• May present to the ED with pallor, poor feeding, tachycardia, respiratory distress
• Check hemoglobin in any HDFN infant readmitted for any reason

Differential diagnosis

Neonatal jaundice within 24 hours

• HDFN (ABO, Rh, minor antigens) — this page
• G6PD deficiency — most common enzyme deficiency causing neonatal hemolysis worldwide; often triggered by oxidative stress; Coombs-negative
• Hereditary spherocytosis — family history; spherocytes on smear; Coombs-negative; osmotic fragility increased
• Sepsis — ill-appearing; fever or hypothermia; WBC abnormalities
• Enclosed hemorrhage (cephalohematoma, subgaleal hemorrhage) — resorbing blood → bilirubin production; no hemolysis markers
• Crigler-Najjar syndrome — unconjugated hyperbilirubinemia without hemolysis (normal reticulocyte count, Coombs-negative, normal haptoglobin)
• Pyruvate kinase deficiency — rare; chronic hemolytic anemia; Coombs-negative

Key distinguishing features of HDFN

• Positive direct antiglobulin test (DAT/Coombs) — confirms antibody on neonatal RBCs (though may be weakly positive or negative in ABO disease)
• Blood type mismatch between mother and infant
• Elevated reticulocyte count (appropriate marrow response to hemolysis)
• Spherocytes on peripheral smear (especially in ABO incompatibility)

Evaluation

ED workup

• Fractionated bilirubin (total and direct): expect predominantly unconjugated
• Maternal and infant blood type and Rh: identifies the incompatibility
• Direct antiglobulin test (DAT/direct Coombs test): positive confirms antibody coating neonatal RBCs
  • Strongly positive in Rh disease; may be weakly positive or negative in ABO disease (does not exclude ABO HDFN)
• CBC with reticulocyte count: anemia + elevated reticulocytes (expect >5-10%; may be markedly elevated)
• Peripheral blood smear: spherocytes (especially ABO); nucleated RBCs (erythroblastosis); polychromasia
• Haptoglobin, LDH: hemolysis markers (haptoglobin low, LDH elevated)
• Albumin level: low albumin reduces bilirubin binding capacity and lowers the threshold for kernicterus
• Blood glucose: neonates with hemolytic disease may be hypoglycemic

Additional testing

• Maternal antibody screen (indirect Coombs test): identifies circulating maternal antibodies; identifies non-D alloantibodies (Kell, Duffy, etc.)
• Antibody identification panel: if indirect Coombs is positive, to identify specific antibody
• Cord blood bilirubin (if obtained at delivery): >3.5 mg/dL suggests significant hemolysis

Interpreting the bilirubin

• Use hour-specific bilirubin nomograms (Bhutani nomogram) — plot the bilirubin level against the infant's age in hours to determine risk zone
• Neurotoxicity risk factors that lower the treatment threshold: prematurity (<38 weeks), isoimmune hemolytic disease (positive DAT), G6PD deficiency, asphyxia, sepsis, acidosis, hypoalbuminemia (<3 g/dL)

Management

Phototherapy

• Initiate immediately for any neonate with HDFN and bilirubin at or approaching the phototherapy threshold for age
• Intensive phototherapy: high-irradiance blue LED light (460-490 nm); maximize skin surface exposure
• Phototherapy converts unconjugated bilirubin into water-soluble photoisomers excreted without hepatic conjugation
• Continue until bilirubin is well below the exchange transfusion threshold and declining
• Phototherapy indications specific to HDFN (more aggressive than non-hemolytic jaundice):
  • Cord bilirubin >3.5 mg/dL: start immediately
  • Bilirubin rising >0.5 mg/dL/hour despite phototherapy: escalate to intensive phototherapy and prepare for exchange transfusion

Intravenous immunoglobulin (IVIG)

• IVIG 0.5-1 g/kg IV if bilirubin is rising rapidly (>0.5 mg/dL/hour) despite intensive phototherapy, or if bilirubin is approaching exchange transfusion threshold
• Mechanism: blocks Fc receptors on neonatal reticuloendothelial cells → reduces antibody-mediated RBC destruction
• May avoid the need for exchange transfusion (NNT ~3-6)
• Can repeat once if needed
• Caution: rare but reported association with necrotizing enterocolitis (NEC) in late preterm/term infants

Exchange transfusion

• Definitive emergency treatment for severe HDFN with dangerously elevated bilirubin or signs of acute bilirubin encephalopathy
• Double-volume exchange (twice the infant's blood volume, ~160-170 mL/kg)
• Removes: circulating unconjugated bilirubin, antibody-coated RBCs, and free maternal antibodies
• Replaces with: fresh donor RBCs that lack the offending antigen
• Blood selection:
  • Rh disease: O-negative, Rh-negative, crossmatched against maternal serum
  • ABO disease: O-type RBCs with AB plasma (or type-specific), Rh-compatible
  • All blood should be irradiated and leukodepleted
• Indications:
  • Cord hemoglobin <10 g/dL with hydrops
  • Bilirubin rising >0.5 mg/dL/hour despite intensive phototherapy + IVIG
  • Bilirubin at or above the exchange transfusion threshold for age on nomogram
  • Any signs of acute bilirubin encephalopathy (lethargy, opisthotonus, seizures)
• Give IV albumin 1 g/kg before exchange transfusion (binds free bilirubin, increases efficiency of exchange)

Simple transfusion

• For significant anemia (hemoglobin <7-10 g/dL depending on clinical status) without dangerously elevated bilirubin
• Also for late anemia on readmission (ongoing hemolysis after initial hospitalization)
• Use irradiated, leukodepleted, antigen-negative packed RBCs

Supportive care

• IV dextrose-containing fluids (prevent hypoglycemia; maintain hydration)
• Frequent bilirubin monitoring (every 4-6 hours during active hemolysis)
• Monitor hemoglobin serially (hemolysis is ongoing)
• Iron supplementation (after acute phase; hemolysis depletes iron stores)
• Folic acid supplementation
• Avoid medications that displace bilirubin from albumin: sulfonamides, ceftriaxone, salicylates

Disposition

• All neonates with confirmed HDFN and significant hyperbilirubinemia: admit
  • NICU if exchange transfusion anticipated, hydrops present, or signs of encephalopathy
  • Well-baby unit with continuous phototherapy if mild-moderate disease
• Readmission for late anemia: admit if symptomatic anemia; transfuse as needed; discharge with close hematology/pediatric follow-up and planned hemoglobin checks at 1-2 week intervals
• Discharge criteria after acute HDFN:
  • Bilirubin declining and below phototherapy threshold
  • Hemoglobin stable and adequate
  • Feeding well
  • Arrange follow-up hemoglobin check within 48-72 hours (and again at 1-2 weeks) — late anemia is common and frequently missed
• Prevention counseling (Rh disease):
  • Ensure Rh-negative mothers receive anti-D immunoglobulin (RhoGAM) at 28 weeks gestation and within 72 hours of delivery of an Rh-positive infant
  • Also indicated after miscarriage, ectopic pregnancy, amniocentesis, abdominal trauma, or any event that may cause fetomaternal hemorrhage

See Also

• Neonatal jaundice
• Kernicterus
• Neonatal hepatitis
• Crigler-Najjar syndrome
• Gilbert syndrome
• G6PD deficiency
• Hereditary spherocytosis
• Hydrops fetalis

External Links

• StatPearls — Hemolytic Disease of the Fetus and Newborn
• Arch Dis Child — Haemolytic disease of the newborn (2007)
• Medscape — Hemolytic Disease of the Newborn Treatment & Management
• MedlinePlus — Hemolytic disease of the newborn