Has anti-D prophylaxis increased the rate of positive direct antiglobulin test results and can the direct antiglobulin test predict need for phototherapy in Rh/ABO incompatibility?

Aim: To determine the impact of Rhesus (Rh) D prophylaxis on positive direct antiglobulin test (DAT) results and ability of a DAT grade to predict an infant's need for phototherapy. Methods: Laboratory and infant medical records were reviewed for DAT status, DAT grade, interventions for hyperbilirubinemia including phototherapy, blood transfusion, exchange transfusion and intravenous immunoglobulin. Two epochs of DAT results were reviewed, the first in the era prior to Rh D prophylaxis, the second after introduction of standardised Rh D prophylaxis for Rh negative women. Results: A total of 165 DAT-positive infants' medical records were reviewed. The number of positive DAT results increased from 1.5% to 2.3% (P < 0.0001) following introduction of anti-Rh D prophylaxis, the increase related to an increase in anti-D DATs (7.4% to 32% -P < 0.0001). An infant with a DAT grade of 5-8 was 2.6 times more likely to need phototherapy than an infant with a DAT grade of 2-4 (odds ratio (OR), 2.571; 95% confidence interval (CI), 1.225-5.393; P = 0.08) and an infant with a DAT grade of 10-12 was 4.7 times more likely to need phototherapy than an infant with a DAT grade of 2-4 (OR, 4.724; 95% CI, 1.602-13.926, P = 0.013). Conclusions: Rh D prophylaxis has increased positive DAT results, which may increase the number of unnecessary bilirubin measurements. A low or high DAT grade is strongly predictive of whether an infant does or does not require phototherapy. However, an intermediate DAT requires concomitant bilirubin measurements to determine phototherapy requirements.