The Chido (Ch) and Rodgers (Rg) blood group system (ISBT 017) consists of 9 antigens.
- Chido Antigens:
- Ch1, Ch2, Ch3, Ch4, Ch5, and Ch6.
- 97% frequency of occurrence in most populations.
- Anti-Ch was first discovered in 1967.
- Rodgers Antigens:
- Rg1 and Rg2
- 97% frequency of occurrence in most populations.
- Anti-Rg was first discovered in 1976.
- WH Antigen
- 15% frequency of occurrence in most populations.
Disease Association
Rather than residing on the red cell membrane, the antigens in this blood group system are located on a protein called complement component C4, which circulates in the plasma and binds with the red cells. There are several notable disease associations with this blood group system; people who are Ch- (lack C4b) are more susceptible to bacterial meningitis and people who are Rg- (lack C4a) are more susceptible to Systemic Lupus Erythematosus (SLE).
Patients with antibodies to Chido and Rodgers system antigens typically can safely receive any ABO/Rh compatible RBCs for transfusion, however, there have been reported cases of significant reactions to plasma and platelet transfusions in these patients.
Treatment
This blood group system is sensitive to enzyme treatment, such as papain or ficin, sensitive to trypsin and alpha-chymotrypsin, and resistant to disulfide-bond reducing agents such as Dithiothreitol (DTT) or 2-aminoethylisothiouronium bromide (AET), resistant to Chloroquine Diphosphate (CDP) treatment, and resistant to EDTA Glycine-Acid (EGA) treatment.
Common Findings
Since the Ch and Rg antigens are present in the plasma of approximately 97% of the population, you can neutralize a demonstrating Ch or Rg antibody by adding an equal volume of pooled normal plasma to the plasma containing the antibody. This is effective because pooled normal plasma should contain sufficient Ch and Rg antigens to adsorb the circulating antibody and resolve the interference from the anti-Ch or anti-Rg. It is important to run a suitable control in parallel to verify that the lack of reactivity is not due to dilution of the antibody when performing this technique, such as patient plasma pooled with an inert control like bovine albumin.
