The search for rare blood donors among native Americans.
The problem has to do with Diego, the ninth genetically independent red cell antigen system discovered. It has two alleles: Di.sup.a and Di.sup.b. Most people, including all Caucasians and blacks, are Di(A-b+). But a few American Indians and other persons of Mongolian ancestry are (Di(a+b+); an even smaller fraction is Di(a+b-). Transfusing a Di(a+b-) patient who has formed the antibody to Di.sup.b becomes an acute emergency because there are fewer than 20 known Di(a+b-) donors in the United States.
Our Tulsa-based region of the American Red Cross has been aware for some time that rare donor registries desperately needed more Diego b negative donors. We thought we might be able to expand the list. About two-thirds of the state's estimated 180,000 native Americans reside in our 32-county collection area in eastern Oklahoma, including the largest concentration of Indians from the five civilized tribes--Cherokee, Creek, Choctaw, Chickasaw, and Seminole.
When we decided on a Diego b negative screening program, we first considered initiating it at the Indians' annual pow-wow. Upon reflection, however, blood drawing seemed out of place at this primarily cultural and social gathering. It would be better to incorporate the screening effort into our regular collection schedule. While canvassing our large section of the state, we would ask regular and first-time donors to participate in this voluntary project.
The first step in developing the screening program was to obtain endorsements from the highly influential principal chiefs, or tribal leaders. Then we carefully prepared literature and posters to explain both the screening program and our motives. We stressed the importance of locating rare blood that could help save others in the Indian community. We had to emphasize the humanitarian rewards of participating and make sure that no aspect of the program could be misconstrued as experimentation.
We began by contacting the Indian Health Service in Oklahoma City and outlining our plan to the chief technologist. With his backing, we approached the Principal Chief of the Cherokee Nation. The chief quickly understood why the program was needed and gave us the endorsement shown in Figure 1. At his request, we met with blood bankers from a clinic serving the Cherokee region to brief them on the program and answer any questions.
With this accomplished, we tackled our promotional campaign. A large poster seemed the best way to attract attention and explain the need for the study and its benefits. The poster featured a portrait of a young Indian woman, the Chief's endorsement letter, and our consent form.
The search for rare Diego b negative donors officially began in September 1982, with a blood-mobile visit to the town of Tahlequah, where the Cherokee Nation tribal complex is located. The 3 X 4-foot poster was prominently displayed at the entrance to the collection area, allowing donors to ponder the screening program while completing the standard health history questionnaire. Nurses and technologists were available to answer any questions, and to ask whether donors were interested in the program.
Those interested in participating then filled out the form shown in Figure II. This form, which identifies any donors who subsequently prove to be Diego be negative, includes a brief explanation of the program and a thank-you from the staff. We are especially interested in calculating each participant's fraction of Indian heritage, based on tribal parentage and grandparentage, for reasons we'll explain shortly.
The screening program's debut was a resounding success. All who donated during the Tahlequah visit agreed to participate in the survey. We hadn't anticipated such complete acceptance of the program. The enthusiasm and appreciation encountered at the Cherokee complex gave us impetus to carry the study throughout our collection area.
Our Diego b negative search just celebrated its second anniversary, and we have now tested more than 4,000 Indians representing 30 different tribes (Figure III). Because of the rarity of the Diego b antisera, all participants--whether 1/64 or full-blooded Indian--are first tested for the presence of the Diego a antigen. Those demonstrating a positive result for Diego a have a possibility of being negative for Diego b and are subsequently screened for this antigen.
The procedure for identifying the Diego b antigen is fairly simple. We use typing trays and add one drop of the antiserum and one drop of the cell suspension. After incubating the mixture for 30 minutes at 37 degrees, we wash the cells and add Coombs serum, which detects a positive or negative reaction. To conserve antisera, we use the microplate method for all testing.
Fifty of our 4,000 participants so far have been found to be Diego a positive and have undergone additional screening; four were ultimately classified as Diego b negative, the rare potential donors we were seeking. The highest percentages of Di.sup.a + participants were found among the following tribes: Creek (11 per cent), Choctaw (5 per cent), and Cherokee (4 per cent). The four Di.sup.b.--participants were a full-blooded Sioux, a Pawnee, a Creek, and a Shawnee/Seminole.
We conduct further screening for 22 other significant red cell antigens on any participants who are at least three-fourths Indian--a point established by tracing their tribal heritage back to their grandparents. That covers most participants in the program. In this phase of screening, we hope to determine eventually whether certain tribes have a greater tendency to be either positive or negative for the various antigens.
While it's too early to draw any definitive conclusions, certain trends have emerged among the
Indian population we serve. For example, 87 per cent of the Creeks tested were type O, compared with 68 per cent of the Cherokees and 73 per cent of all other tribe members. Four per cent of the Creeks were type A, compared with 24 per cent of both the Cherokees and all other tribe members.
With regard to Rh typing, all of the Creeks and 98 per cent of the others were Rh positive. One interesting finding was that three participants were R.sub.Z.R.sub.Z.. That's a small number, but high in comparison to Caucasians. It would be necessary to test 500,000 Caucasians to find three R.sub.Z.R.sub.Z positive subjects.
Although we have reached most of our regular donors during the past two years, we're still signing up new participants. The program has worked so well that few changes have been needed. We did, however, design a new poster (see below). This smaller, more manageable version looks more professional than its predecessor, and we now distribute copies in advance of the bloodmobile's arrival.
Certainly a large number of Indians remain to be studied. In the future, we hope to shed new light on gene frequencies and to contribute other anthropological information. In conjunction with the Diego screening study, we plan to begin HLA typing to correlate disease to various HLA antigens.
In the meantime, we have begun building an inventory of frozen rare red cell units for future use. We have also listed the four Diego b negative potential donors with registries in the United States.
None of our patients has needed the rare blood yet. But we were able to help the American Red Cross donor registry in Washington, D.C., when a woman of Peruvian descent suffered a subdural hemorrhage. Surgery was delayed while the blood bank tried to locate Diego b negative blood. The registry contacted our facility, and we immediately shipped six units to the waiting hospital, hundreds of miles away. The patient's recovery was the most tangible reward imaginable for our time and trouble.
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|Author:||McClintock, Clarissa; Crow, Martha; Lawson, James; Kasprisin, Duke O.|
|Publication:||Medical Laboratory Observer|
|Date:||Oct 1, 1984|
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