Chemically Modified Anti-D

Constituents This antiserum contains an IgG anti-D that has been chemically modified to increase the span of its Fab fragments, and a low protein concentration of 6 - 8%. (Note: Some commercial chemically modified anti-D sera have an intermediate protein concentration of about 10 - 15%).

Preparation Method The antiserum is made by treating IgG anti-D with sulfhydryl agents. These agents split the interchain disulphide bonds that hold the heavy chains together and allow the two Fab fragments to span a wider distance and agglutinate red cells suspended in saline. Because reoxidation can cause the disulphide bonds to reform, the disulphide reduction is made permanent by alkylation with iodoacetamide.

Indications for Use
Chemically modified anti-D can be used as follows:

1. as an alternative to saline anti-D for typing red cells with a positive DAT (both have a low protein concentration);
2. for routine D typing as an alternative to slide and modified tube anti-D;
3. for weak D (D^u) typing (since it is IgG).

Mechanism As described above, the IgG anti-D molecules have a span that is sufficient to allow them to agglutinate cells suspended in saline. The low protein (6 - 8% albumin) is added to help stabilize the antibodies.

Rh Control The forward ABO group can serve as a control. In AB patients, an Rh control of 6% albumin should be tested in parallel with the D typing. Although it is unlikely that red cells with a positive DAT will spontaneously agglutinate in a low protein medium, if they are heavily sensitized, they may.

Chemically Modified Anti-D