Review of positive direct antiglobulin tests found on cord blood sampling

Abstract

Until recently, all babies born in Wellington had umbilical cord blood sampling for direct antiglobulin test (DAT). It is considered to be an important test in identifying babies who are at risk of haemolytic disease of the newborn (HDN).

Objective: The aim of this review was to examine the utility of positive DAT results and ascertain: -- How many cases required phototherapy? -- Were any babies readmitted for phototherapy? -- Did the positive DAT influence the detection and treatment of HDN?

Methods: The clinical records of all newborn babies found to have positive DATs by Wellington Hospital Blood Bank, over a 6-month period (January 2001-June 2001) were reviewed. Blood group serological results of all babies that received phototherapy during this period were also reviewed.

Results: Ninety-four babies had a positive DAT, of which 22 (23%) received phototherapy. The incidence of a positive cord blood DAT was found to be 5.5%. In total, 1724 cord blood samples were analysed by Blood Bank over the first 6 months in 2001. Overall 145 babies received phototherapy, 117 were DAT-negative and six were not tested. Six of the 22 (27%) DAT-positive babies that received phototherapy were alerted by a positive DAT, leading to measurement of serum bilirubin (SBR). Twelve of the 22 (55%) were initially alerted by clinical jaundice, leading to measurement of SBR. Two DAT-positive cases were diagnosed antenatally, both were due to anti-D. Overall 10 babies were readmitted for phototherapy, two had a positive DAT. One baby received an exchange transfusion in addition to phototherapy. Two babies that received phototherapy had SBRs in the exchange transfusion range. Eighty-six per cent of the DAT-positive cases treated with phototherapy were due to anti-A. There were four cases of DAT-negative ABO HDN.

Conclusions: The positive predictive value of a positive DAT for HDN is 23%. The sensitivity was estimated to be 86%. Ten babies required readmission for phototherapy, two of these were DAT-positive. Jaundice, rather than the positive DAT, was the first alert in the majority of cases of HDN requiring phototherapy. Recommendations for testing are discussed but remain controversial in practice. Assessment for hyperbilirubinaemia in all infants early in life is fundamental.