Blood Donor Reservoir Running Low

MINNEAPOLIS, Aug. 2 -- Progressively more stringent safety standards for blood donation have unexpectedly cut the national donor pool to 37.8% of the U.S. population, researchers here found.

Previous estimates, which used only age as an exclusion criterion, had overestimated the eligible population by 59% and therefore underestimated voluntary donation rates by the same proportion, said Jeffrey McCullough, M.D., of the University of Minnesota, and colleagues.

Their study evaluating population prevalence of 31 exclusionary factors turned up 111 million eligible donors rather than the projected 177 million, they reported in the July issue of Transfusion.

The findings "should assist in calculating blood donor rates, forecasting blood supply shortages, and designing donor recruitment strategies," they wrote.

The number of potential donors turned away at the door because of self-reported exposures, medical evaluation, previous screening results, or a prior deferral has been well known.

But, "many people are aware that they should not donate blood and thus do not present themselves to the blood bank," the researchers noted.

Therefore, the impact of progressively increasing exclusion criteria over the past two decades to reduce the risk of transfusion-transmitted disease and improve donor safety has not been well characterized, the investigators said.

They estimated donor ineligibility for 31 factors from the standards of the AABB (formerly known as the American Association of Blood Banks) using epidemiologic data from government agencies and disease- or disorder-specific advocacy organizations.

After the exclusions were adjusted for annualization, they estimated that 47.8% of age-eligible Americans (18 to 65 based on conventional estimates and data availability) would be deferred from voluntary blood donation. The findings were:

• 53.9 million excluded because of permanent issues, such as heart disease, travel to a region where malaria is endemic, and cancer.
• 12.6 million prohibited for issues that would take them out of the potential pool for three months to a year, such as pregnancy, a tattoo, or tuburculosis.
• 18 million excluded for short-term issues like anemia, lack of diabetes control, or illness.

When these rates were further adjusted to account for overlapping conditions in the same individual using probability calcuations, the final prevalence of donor exclusions within the age-eligible population was 37.23%.

Their model thus added 66 million to the conventional estimate of 117 million ineligible individuals out of the 294 million U.S. population and reduced the estimated eligible donor population from 60.2% to 37.8%.

Dr. McCullough and colleagues noted that voluntary blood donor rates rise dramatically in light of the new estimates.

Using their model, the voluntary blood donation rate was about 128.8 units of blood per 1,000 eligible donors in 1999 compared with the previously reported 80.8 units per 1,000, which is a 59% increase, they said.

However, the researchers noted, some of their assumptions require further validation. These include the use of standard distribution rather than epidemiologic prevalence data to determine the probability of overlapping conditions.

Also, they acknowledged, they did not look at social and demographic factors affecting blood donation because they only considered safety exclusions.

And, they were unable to obtain data for some potentially significant exclusions, including vaccination, blood donation in the prior eight weeks, transplantation, transfusion, piercing, and use of certain prescription medications.

Still, the findings may be a substantial improvement over prior estimates, Dr. McCullough and colleagues said.

"An accurate estimate of eligible blood donors in the general population is urgently needed to understand whether blood-donation rates are declining as a function of lapses in donor interest or an increase in donor exclusions," they wrote.