Constituents This antiserum contains an IgG anti-D in a protein concentration of about 22 - 30%. Most of the protein consists of albumin, but other antibody potentiators (e.g., PVP or dextran) may be present.
Synonyms include high protein anti-D, incomplete anti-D, and anti-D for slide and rapid tube test.
Indications for use This anti-D was once one of the most commonly used antisera for D typing and it is still used by some labs today. It is relatively inexpensive because a large source of donors still exists (mainly Rh(D)-negative women who have produced anti-D as a result of pregnancy in the years before Rh immune globulin was available). Because it is IgG, it can also be used for weak D (Du) typing.
Mechanism Because IgG anti-D cannot directly agglutinate red cells suspended in saline, the manufacturer adds a high concentration of albumin. The albumin (being a dipolar molecule) increases the dielectric constant and decreases the zeta potential, allowing the red cells to come closer. Once this occurs, the IgG anti-D that has attached to D-positive red cells can form cross-bridges and agglutinate the red cells.
Rh Control This control must be done in parallel with all Rh(D) typing tests. The Rh control is an autocontrol that reveals whether or not the patient's red cells are agglutinating in the absence of the D antigen, i.e., are clumping whether they are D-positive or D-negative. The control consists of testing the patient's cells with an Rh control medium (supplied by the manufacturer) that contains everything that is present in the anti-D typing sera except the anti-D.
The Rh control is essential because red cells that are presensitized with antibody in vivo (i.e., have a positive DAT), can be caused to agglutinate in a high protein medium, even if they are D-negative. When the high protein in the anti-D brings the cells close together, any antibody already on the cells can form cross-bridges and cause a false positive.
If the Rh control is positive, the D typing result is invalid. The Rh(D) type must then be determined using a low protein anti-D serum, e.g., saline anti-D, chemically modified anti-D, or monoclonal/polyclonal anti-D as described below.
|Slide and Modified Tube Anti-D|