57 A Mini Panel for Passive Anti-D (RhIg)

Principle

Once RhIg administration has occurred future antibody screen testing may test positive often up to one month post administration. The date of RhIg is available in the transfusion history. In such cases the antibody titre is very low and usually mimics the presence of a weak Anti-D.  To eliminate the possibility of an alloantibody (agglutination due to an antibody other than RhIg) a mini panel should be performed.

Specimen

Patient plasma (serum)

Reagents 

1. Reagent red cell panels of 4 to 6 cells are now available from manufacturers to identify anti-D and screen for other clinically significant antibodies when RhIg has been administered and an antibody screen is needed.
2. When a specific panel (#1)is not being used “rr” red cells from either the screening cells or panels can be selected for use. Their antigens must be documented on the special investigation worksheets and should include antigens for the presence of common antibodies.
3. One “D” positive cells must also be included.
4. Example:IWK Pathology and Lab Medicine list the following “minimum” requirements:

• • 1 Ror cell
  • 2 r’r cells (students labs will use one cell)
  • 2 r”r cells (student labs will use one cell)
  • 2 rr cells that are K+ (if SIII is K+ only need 1 more in panel)
  • There must be at least 2 each of the following among the D neg cells: Fy(a+), Fy(b+), Jk(a+), Jk(b+), S+, s+. If the cells above do not cover all of these antigens, additional cells are required.
  • If the initial screen results are very weak, especially if the SII is the only reaction, it is advisable to set up a second R2R2 cell. If the initial screen results are 2+ or more, the Ror cell above is not required.

Procedure

1. Follow the SOP for antibody identification but use the selected cells for the mini panel. Student requirements for choosing cells differ slightly from IWK requirements.

Interpretation

1. If all of the “D” negative cells are negative with the patients’ plasma and the “D” positive cells are positive, it is assumed there are no other alloantibodies present along with the passive anti-D. It should be recorded as “weak anti-D demonstrable, probably passively acquired: Rh immune globulin issued on:_________________”