Saline Anti-D

Constituents This antiserum contains IgM anti-D suspended in a protein concentration of about 6 - 8% albumin.

Synonyms include low protein anti-D and complete anti-D.

Indications for use Saline anti-D is usually used to D type red cells that give a positive Rh control when tested with slide and modified tube anti-D, e.g., to D type cells with a positive DAT. Some labs may use it routinely, but it is a relatively expensive antiserum because donors are hard to find (IgM anti-D usually only is produced in a 1° immune response, and Rh immune globulin largely prevents anti-D production as a result of pregnancy). Note: saline anti-D, being IgM, cannot be used for Du typing. Also, it requires a longer incubation time (15 - 60 minutes) and the agglutinates tend to disperse easily.

Mechanism Because the anti-D is IgM, the antibody is large enough to span the distance between red cells suspended in saline. No protein is required to decrease the ZP and bring the cells closer. A protein concentration of 6 - 8% is added to the anti-D only to stabilize the antibody. Note: "Saline anti-D" means that the anti-D is saline-reactive, not that saline is a constituent of the antisera.

Rh Control The forward ABO group can serve as a low protein Rh control. Alternatively, an Rh control of 6% albumin may be tested in parallel since saline anti-D contains 6 - 8% albumin. The control is necessary (especially in apparently group AB patients) because some red cells, if they are heavily sensitized with antibody, may spontaneously agglutinate even in low protein media such as is present in anti-A, anti-B, and saline anti-D.

Saline Anti-D

©1999 Division of Medical Laboratory Science
University of Alberta