[Positive Coomb's test in newborns; causes and clinical consequences Summary of cases diagnosed in the Blood Bank in the years 2005 to 2012].

INTRODUCTION: Hemolytic disease of the fetus and newborn (HDFN) is caused by the destruction of fetal red blood cells due to red cell antibodies produced by the mother. HDFN can cause fetal hydrops during pregnancy or neonatal jaundice after birth. Direct Antiglobulin Test (DAT) detects antibodies bound to red cells and is a valuable test aiding in the diagnosis of HDFN. In Iceland DAT is routinely performed on cord blood or newborn blood samples if the mother is Rhesus D negative or has non-A/B red cell alloantibodies. The aim of this study was to investigate the causes and consequences of positive DAT in newborns in Iceland over a period of eight years.

MATERIAL AND METHODS: The study population was infants diagnosed with a positive DAT in the Blood Bank in Iceland in the years 2005-2012. Relevant data on the blood group and antibody status of mother and child, blood transfusion and DAT results were retrieved from the Blood Bank information system ProSang. Birth records provided information on birth weight, gestational age and phototherapy. Health records from the Children's Hospital provided information on the management and fate of the newborn.

RESULTS: Over the study period 383 newborns had a positive DAT result at the Blood Bank. In 73.6% of cases the underlying cause was ABO blood group mismatch between mother and infant, in 20.4% of cases the mother had non-A/B red cell alloantibodies, in 3.9% both of above factors were present, while in 2.1% the cause was unclear. A total of 179 (47.6%) children had neonatal jaundice that required treatment, of which 167 (93.3%) only needed phototherapy. Eight infants required exchange transfusion, five of these had Rhesus antibodies and three ABO blood group mismatch.

CONCLUSION: ABO blood group mismatch between mother and child was the most common cause for a positive DAT in neonates in Iceland in the years 2005-2012. Almost half of the neonates required treatment but usually phototherapy was sufficient. Rarely, blood transfusion or exchange transfusion was necessary in severe cases of ABO blood group mismatch or non-A/B red cell alloantibodies.

KEY WORDS: Coombs test, Direct Antiglobulin Test (DAT), Hemolytic disease of the fetus and newborn (HDFN), ABO blood group mismatch, red cell alloantibodies, neonatal jaundice, exchange transfusion. Correspondence: Anna Margret Halldorsdottir, [email protected].