Why the Blood Donor Pool is Shrinking:
Estimating the Prevalence of Donor Exclusion Factors on the Pool of Potentia

By William Riley
Associate Professor
Division of Health Policy and Management

Background

Efforts to ensure donor and recipient safety have reduced the population of eligible voluntary blood donors. The pool of potential blood donors traditionally has been calculated based on the population from ages 18 to 65. But many of those people are screened out. There are 31 factors -- ranging from recent tattoos to HIV infection to heart disease -- that either make a person's blood unsafe or make it unsafe for a person to donate blood. Until now, estimates of the U.S. blood-donor pool failed to take these factors into account. These rules were created to ensure that the blood supply is safe, but they also make it tougher for blood banks to meet their goals. This is the first study to look at the aggregate effect of this screening.

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In conjunction with Jeffrey McCullough MD of the University of Minnesota Medical School,  we developed an epidemiological model to determine the prevalence of donor exclusions and thus improve the estimate of total eligible blood donors in the nation.

Study Design and Methods

Epidemiological databases were selected to enumerate the population prevalence of 31 donor deferral factors which correspond to the American Association of Blood Banks (AABB) standards. These 31 deferral factors are used to determine who would be eligible to donate blood.  Prevalence data were adjusted for age, duration of exclusion and co morbidities.  This method yields the number of excluded individuals to calculate the number of eligible blood donors.

Results

The conventional method of calculating eligible donors indicates there are 176.8 million eligible blood donors in the U.S. population.  Our study indicates this methodology erroneously includes 65.8 million individuals who are ineligible due to known exclusionary factors.  Only 111 million individuals in the U.S. population are eligible to donate blood. This means estimates of the number of Americans eligible to donate blood are off by as much as one-third. Only 37 percent of Americans are considered acceptable donors, although it has long been believed 60 percent were eligible.

Conclusion

This study determines the prevalence of donor exclusion factors in the total population and estimates the pool of eligible donors in the nation.  This model, which measures exclusions based on AABB donation standards, is a more accurate method for determining eligible blood donors. U.S. blood centers have been operating under the assumption that 177 million Americans could give blood, but we believe this is a gross overestimate.

We suggest that blood collection organizations develop recruitment strategies which incorporate the results of this study. These strategies are essential because the size of the eligible donor population is projected to decrease over the next decade. The results can also be used  by social scientists to explore novel ways to get more eligible donors to give blood.

Findings of this study were published in the July 2007 issue of Transfusion, the journal of the American Association of Blood Banks.