What additional testing should be done on the neonatal specimen?

  1. Rh-negative neonates born to Rh negative mothers should be tested for the weak D antigen. See RT.003.
  2. A Kleihauer-Betke test should be done.

In this case the neonate’s cells cannot be tested for the presence of weak D because of the positive direct antiglobulin test (would yield a false positive result).

Many laboratories choose to perform a rosette test to screen for fetal cells in maternal circulation, and, if positive,  a Kleihauer-Betke test to determine the quantity of fetal cells in maternal circulation and the amount of Rh immune globulin to be given to the mother.

In this case, what to do is unclear as the neonate appears to be Rh negative by direct agglutination. Additional testing should be done in consultation with a laboratory physician. Other determining factors may be considered at this point such as the Rh of the father. If the laboratory has the ability and reagents, the neonatal cells could be treated with chloroquine disulphate to remove the bound antibody and weak D testing performed. This is usually not done routinely.