New laboratory procedures and Rh blood type changes in a pregnant woman

A woman's candidacy for Rh immune globulin depends on whether her blood type is Rh-positive (D antigen-positive) or Rh-negative (D antigen-negative). New molecular blood-typing methods have identified variant D antigens, which may be reported as Rh-positive or Rh-negative depending on the laboratory method. We describe a case illustrating the effect of the new laboratory methods on a woman's candidacy for Rh immune globulin and present recommendations for interpreting the new test results.

A 40-year-old woman presented for management of her third pregnancy. During her first pregnancy, she was typed as Rh-positive ("D") and did not receive Rh immune globulin. During her second pregnancy, she was typed as Rh-negative, in accordance with revised Rh-typing procedures. Anti-D antibody was detected. During her third pregnancy, she was genotyped as a partial D antigen, which was reported as Rh-negative.

Revisions in laboratory procedures for Rh typing may present as a change in the Rh blood type of pregnant women-and as a change in their eligibility for Rh immune globulin.