Before allowing a blood transfusion or organ transplant, it is critical to ensure that the donor’s blood or organ is not coated with antigens for which the recipient has antibodies for. As described in earlier blog posts, there are two sets of antigens that are important to test for, blood group and human leukocyte antigens (HLAs). Currently, the test for blood type costs about $10 to $20. This is reasonably low for a one-time test. But is too expensive to do repeatedly. Thus, if you are a regular blood donor, like me, they always ask you for your donor card which contains your blood type, rather than test it each time.
The cost of HLA testing is even higher. There are many genes involved with names like A, B, Bw, Cw, DP, DQ, DR, DR51, etc. Each gene has several possible allotypes, each identified by a one to four digit number like 7, 8, 27, 2701, etc. For a list of all the variations, see Wikipedia and NKR. Currently, the test to identify the allotype of a single HLA gene costs between $100 to $200 per person and requires a skilled technician with access to a lab. Each transplant center has its own requirements for which HLAs need to be identified. There can be up to 10 HLA tests required, for a total cost of $1,000 to $2,000 per potential donor.
Even a $10 test is expensive for patients in lesser developed countries. A $1,000 test, which can represent a year’s cash income, is unaffordable for patients in most parts of the world.
Yesterday, Tech. Rev. reported that Gil Garnier and his colleagues at Monash Univ. in Australia have developed a low-cost, paper-based blood type test (Analytical Chem. May 2010, subscription required). The antibodies are applied to the paper substrate using a modified ink jet printer. Running the test only requires a single drop of blood. If the blood agglutinates and does not spread, then the antigen in the blood reacted with the antibodies on the paper. If the blood spreads, then it means no reaction occurred. The example below shows the results for a person with blood type A RhD+.
Besides using only a small amount of blood, another benefit of this new test is that it can be conducted in the field without any additional reagents or refrigeration. And finally, in volume, the test is expected to cost less than 10 cents each.
If this technology can be extended to include antibodies for the HLAs, then it would be an excellent way to improve matching of living organ donors to recipients. Currently, transplant hospitals only allow a single donor to be evaluated at a time because of the high costs. With cheaper tests, everyone who is willing to donate could get tested and the person who is the best match would be selected as the final candidate.
Lower cost HLA tests could also dramatically increase the number of people who get on the national bone marrow registry. Currently, the registry needs to balance the cost of finding people willing to sign up to be donors with the cost of conducting HLA tests on the large proportion of participants who will never match a recipient. Lower cost HLA tests could reduce the need for this trade-off.