What does a positive Direct Antiglobulin Test (DAT) indicate in infants?

From the Guidelines

A positive Direct Antiglobulin Test (DAT) in infants is a significant indicator of immune-mediated hemolysis, suggesting that antibodies are attached to the infant's red blood cells, which can lead to hemolytic disease of the newborn (HDN) and requires prompt investigation and management. This finding is most commonly associated with hemolytic disease of the newborn (HDN), where maternal antibodies cross the placenta and bind to antigens on the infant's red blood cells, causing their destruction 1. The most frequent causes include ABO incompatibility between mother and baby (typically mother with O blood type and baby with A or B) or Rh incompatibility (Rh-negative mother sensitized to Rh-positive fetal cells). A positive DAT may also occur in infants receiving incompatible blood transfusions or those with autoimmune hemolytic anemia, though these are less common.

Clinical Implications

Clinical manifestations can range from mild jaundice to severe hemolytic anemia requiring intervention. When encountering a positive DAT in an infant, further investigation should include:

• Blood typing of mother and infant
• Antibody identification
• Bilirubin levels
• Hemoglobin measurement to determine the severity and specific cause of hemolysis and guide appropriate management 1. According to the most recent guidelines, infants with a positive DAT should have a follow-up TSB measure 8 to 12 hours after phototherapy discontinuation and on the following day, and care should be escalated when an infant’s TSB level is at or above the exchange transfusion threshold or within 0 to 2 mg/dL below the exchange transfusion threshold 1.

Management

Management of a positive DAT in infants involves identifying the underlying cause of hemolysis and providing appropriate treatment, which may include phototherapy, exchange transfusion, or other interventions to reduce the risk of severe hyperbilirubinemia and its associated morbidity and mortality 1. It is essential to monitor these infants closely for signs of hemolysis and to adjust management accordingly to prevent long-term sequelae and improve quality of life.

From the Research

Direct Antiglobulin Test (DAT) in Infants

A positive Direct Antiglobulin Test (DAT) in infants indicates the presence of immunoglobulin, complement, or both bound to the red blood cell membrane, which can be a sign of hemolytic disease of the newborn (HDN) [ 2, 3 ].

Causes of Positive DAT

The causes of a positive DAT in infants can be attributed to:

• ABO incompatibility [ 2, 4, 5 ]
• RhD incompatibility [ 2 ]
• Other red blood cell antibodies [ 2 ]

Clinical Implications

A positive DAT can lead to:

• Hemolysis [ 2, 4 ]
• Hyperbilirubinemia [ 2, 4, 5 ]
• Need for phototherapy [ 2, 5 ]
• Need for exchange transfusion [ 4, 5 ]
• Increased risk of severe hemolytic disease of the newborn [ 2, 6 ]

Key Findings

• The prevalence of DAT positivity was found to be 3.3% in a study of 2769 babies [ 2 ]
• The need for phototherapy was significantly higher in DAT-positive infants [ 2 ]
• Severe hemolytic disease of the newborn, bilirubin level, duration of phototherapy, and use of intravenous immunoglobulin were found to be significantly higher in babies whose mothers were IAT positive [ 2 ]