ABO Hemolytic Disease of the Newborn with Positive DAT
The baby's positive DAT and eluate results indicate ABO hemolytic disease of the newborn due to anti-B antibodies from the O positive mother reacting with the B antigens on the B positive baby's red blood cells.
Interpretation of Laboratory Results
The laboratory findings present a classic case of ABO hemolytic disease of the newborn (HDN):
- Mother: O positive with negative antibody screen
- Baby: B positive with 3+ DAT
- Eluate results: Positive reactions with A1, B, and screening cells 1 & 2
- Last wash: Negative (confirming valid test results)
Significance of Findings:
- The 3+ DAT indicates significant coating of the baby's red blood cells with antibodies
- The eluate showing reactivity with B cells confirms anti-B antibodies are responsible
- Reactivity with A1 cells suggests the presence of anti-A antibodies as well, which is typical in O individuals who naturally produce both anti-A and anti-B
Pathophysiology
This represents a classic case of ABO incompatibility where:
- The O positive mother naturally produces IgG anti-A and anti-B antibodies
- These IgG antibodies cross the placenta during pregnancy
- The antibodies bind to the B antigens on the baby's red blood cells
- This antibody binding leads to hemolysis of the baby's red blood cells
Clinical Implications and Management
Immediate Assessment:
- Monitor bilirubin levels every 4-6 hours initially 1
- Plot total serum bilirubin (TSB) on an hour-specific nomogram to determine risk zone
- Calculate rate of bilirubin rise to identify ongoing hemolysis
- Monitor hemoglobin/hematocrit for evidence of anemia
Treatment Approach:
Initiate intensive phototherapy if TSB reaches threshold based on age and risk factors 1
- Use LED-based devices for maximum efficacy
- Ensure maximum skin exposure
- Continue breastfeeding during phototherapy
Consider IVIG administration (0.5-1 g/kg over 2 hours) if:
- TSB is rising despite intensive phototherapy
- TSB is within 2-3 mg/dL of exchange transfusion threshold 1
Prepare for exchange transfusion if TSB reaches ≥25 mg/dL or exchange transfusion threshold 1
- Use O negative RBCs compatible with maternal antibodies
- Blood should be crossmatched against mother's serum, not infant's
- Blood should be irradiated, leukocyte-reduced, CMV-negative, and less than 7 days old
Monitoring Protocol:
- Monitor TSB every 4-6 hours until declining, then every 8-12 hours 1
- Ensure adequate hydration and nutrition
- Discontinue phototherapy when TSB has declined by 2-4 mg/dL below treatment threshold
- Obtain follow-up TSB measurement 8-12 hours after discontinuing phototherapy 1
Risk Factors and Prognosis
Recent research shows that neonates with ABO incompatibility and positive DAT have:
- Higher bilirubin levels at 24 hours (8 ± 2.6 mg/dL vs. 6 ± 2.2 mg/dL in DAT-negative cases) 2
- Higher peak bilirubin levels (12.7 ± 3.6 mg/dL vs. 10.4 ± 4.2 mg/dL) 2
- Higher phototherapy requirement (46.8% vs. 11.2%) 2
- Lower hemoglobin levels 2
Clinical Pearls and Pitfalls
Important Considerations:
- ABO HDN is typically milder than Rh HDN but can occasionally be severe
- In a large Icelandic study, ABO incompatibility accounted for 73.6% of positive DAT cases in newborns, with 47.6% requiring treatment 3
- Exchange transfusion is rarely needed (only 3 of 279 ABO cases in the Icelandic study) 3
Unusual Presentations:
- While O mothers with anti-A/B antibodies are the most common scenario (accounting for ~15% of pregnancies in Caucasians), mothers with blood type A or B can occasionally cause HDN 4, 5
- A case similar to this one was reported where a mother with A2 blood type had high titers of anti-B antibodies causing HDN in an A2B infant with negative DAT, requiring exchange transfusion 4
- Type A or B mothers are 5.5 times less likely to cause sensitization than type O mothers 6