Blood stem cell transplants can be life-saving for some patients, but the chances of finding a matching donor are small unless a large number of potential donors are evaluated. Many nations maintain large registries of potential donors who have offered to donate stem cells if they are the best available match for a patient needing a transplant. An alternative source of stem cells, umbilical cord blood, is stored in banks. Everyone faces a small probability of needing a transplant which will increase their likelihood of survival. The registries and cord blood banks are thus an interesting example of a pure public good with widely dispersed benefits. This paper explores the gains in survival probability that arise from increased registry and bank sizes and uses value of statistical life methods to estimate benefits and compare them to costs. Our results suggest that for the United States and for the world as a whole, the sum of marginal benefits of an increase in either the adult registry or the cord blood bank exceeds marginal costs. However, marginal benefit-cost ratios for the adult registry are much greater than those for the cord blood banks, which suggests that to the extent that these two sources of life saving compete for public funds it may be preferable to prioritize expansion of the adult registry over cord blood banks.
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Formally, donor and recipient must have compatible human leukocytic antigen (HLA) types.
The black population is even more genetically diverse. The probability that two randomly selected individuals are of matching type is less than one in 100,000.
In a later paper, Gragert et al. (2014) used this data to estimate the likelihood of finding perfect matches and acceptable but less than perfect matches for individuals from several racial groups. They did not,however, conduct a benefit-cost analysis or investigate optimal registry sizes.
Operationalizing these innovations required substantial computing resources. The optimum registry calculations were most intensive, requiring approximately 85 Gigabytes of RAM and nearly one week of computer processor time to complete using MATLAB. We are indebted to Wesleyan University for use of a high performance computing cluster that made this possible. The cluster is supported by the NSF under grant number CNS-0619508.
An allele is an alternative form of a gene located at a specific position (genetic locus) in one’s DNA strand. Each locus contains two alleles, one inherited from each of the individual’s parents.
Most of the work on HLA type distributions has treated Hispanic as a “race” rather than an “ethnicity.” We work with this data because it is what is available and use the term “racial group” or “race” to refer to the categories shown in the table. In addition, we hereafter use the term “U.S. Hispanic” since this classification is not made in other countries. Finally, we use the term “black” rather than “African-American” so that we can apply consistent racial labels across countries.
A detailed country-by-country listing of the number of transplants performed, the number of adult donors registered, and the number of cord blood units can be found in Table A.1 of Appendix A. Table 2 excludes the Brazilian registry and cord banks. Although Brazil reports more than three million registrants, the country exported only 3 stem cell products in 2009 (World Marrow Donor Association 2009). We interpret this to mean there are substantial frictions preventing these registrants from being truly available to the remainder of the world. Because Brazil has a large population of African heritage, counting these registrants would have the effect of making the calculated matching probabilities for blacks much higher than is actually observed.
Public data on HLA type distributions is divided into the racial/ethnic categories Caucasian, Black, Asian, and Hispanic but only the United States reports registry totals using these categories. To match the registry data with these categories, we included Pacific Islanders in the Asian category and Native Americans in the Caucasian category. Mixed race individuals were assigned to single races in proportion to the size of each single race group.
For example, see Eapen et al. (2010) and compare Flomenberg et al. (2004) with Barker et al. (2010). Howard et al. (2008) also presented effectiveness scenarios in their sensitivity analysis in which the benefits of 5/6 and 6/6 cord blood transplants were greater than 7/8 adult donor ones, but maintained the preference for 7/8 adult donors in their search algorithm.
Each phenotype can match as many as 8 others at a 7/8 match level; 6 others at a 5/6 match level; and 15 others at a 4/6 match level.
Estimates of these probabilities from a search of U.S. banks alone are found in Appendix C.
Appendix B shows the detailed calculations used to make these estimates.
These figures are based on our estimates of the effects of adding a single registrant or cord blood unit. To make the tables more readily interpretable, we report estimated effects of adding 1,000 adult registrants or 100 cord blood units. The figures in the tables are calculated by multiplying the estimated effects of adding a single adult registrant by 1,000 and of adding a single cord blood unit by 100.
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Howard et al. (2008) provide estimates from cord banks that: (1) 50% of collected units are too small and must be discarded; (2) the cost of processing a unit that is ultimately discarded is $500; and (3) the cost of processing a unit that is ultimately added to the bank is $1500. Together, these figures imply spending $2,000 for each newly banked unit.
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The authors acknowledge support under NSF grant SES-0851357. In addition, we thank Wesleyan University for computer time supported by the NSF under grant number CNS-0619508. We also thank Martin Maiers of the National Marrow Donor Program for several useful discussions about this work. Chelsea Swete provided valuable research assistance. The views expressed in this paper are those of the authors and do not necessarily reflect those of the Federal Reserve Bank of New York or the Federal Reserve System.
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Sheehan-Connor, D., Bergstrom, T.C. & Garratt, R.J. Saving lives with stem cell transplants. J Risk Uncertain 51, 23–51 (2015). https://doi.org/10.1007/s11166-015-9222-7
- Benefit-cost analysis
- Stem cells