Blood Supply Largely Safe, But More Needed
By Rich McManus
As recently as the mid-seventies, about the time the United States adopted a national blood policy (1973), a patient requiring blood transfusion for an operation at the Clinical Center had a one in three chance of contracting hepatitis from the transfusion. Today, thanks to improvements in screening donors and their blood, the rate of transfusion-associated hepatitis at NIH has dropped to virtually nothing.
So reported Dr. Harvey Klein, chief of the Clinical Center's department of transfusion medicine, at a Grand Rounds presentation Mar. 8 on the supply, safety and adequacy of the nation's blood reserve. Klein, who joined DTM in 1973 and has been department chief since 1984, surveyed the horizon of risks associated with blood transfusion, and found most of them on the downsweep.
Hepatitis A is very rarely passed along by blood transfusion; hepatitis B is detectable by two tests, however there is a "window" during which the virus can't be found a new vaccine for hepatitis B should assure that this disease, too, becomes more rare; hepatitis C poses a far lower risk by blood transfusion than it did in the past. "Less than 5 percent of new infections are associated with transfusion," Klein said. Some 200,000 new cases of the illness are, nevertheless, diagnosed each year.
Turning to HIV, Klein noted that 1 in 300 Americans carries the virus. Chillingly, 90 percent of the recipients of HIV-contaminated blood later become infected. Less than 40 HIV infections via transfusion have occurred in the United States since 1985, Klein said. With the reduction of the number of high-risk donors (by pre-donation histories taken by blood bank personnel) and with current sensitive screening tests (of which there are two), the risk is approaching 1 in 1 million, or about that of being struck by lightning, he explained. Similarly, the risk of acquiring hepatitis C by transfusion equates roughly to that of being killed in a train accident in the next year.
Klein then looked at other possible blood contaminants such as retroviruses, parasites, prions and emerging viruses. Malaria, he said, is by far the most important transfusion-transmitted illness on a worldwide basis, but is relatively rare in the U.S. Only 103 cases were reported in the period 1958-1998, making the odds of acquiring malaria from transfusion about 1 in 4 million. However, the malaria parasite can persist in blood for around 40 years, so the possibility of its entering the blood supply is real. "We don't often think about it as one of our risks," Klein observed, "but we have to remain vigilant because the mosquito vector is present in the U.S. We do get 'imported' cases, and it could become a larger problem for transfusion because there are no good screening tests."
Also unusual, but not entirely unknown, are cases of rare strains of HIV that can pass into the blood supply. Klein said a new test that recognizes nucleic acid sequences in the AIDS virus (the NAT test) will help further expunge this risk when it becomes available in a year or so. "We are currently using this NAT technology on an experimental basis on all blood collected at NIH," he said. "I expect the test to be licensed for use across the country within the next year, for both HIV and HCV (hepatitis C virus)."
Interestingly, Britain is now in the throes of concern about the possibility of "mad cow" disease tainting that nation's blood supply. As of March 1999, some 39 people many of them quite young have died from this disease. "(The British) are where we once were with respect to fears of HIV in our blood supply," said Klein. However, no data support the hypothesis that bovine spongiform encephalitis mad cow disease's less daunting name is transmissible by blood. Even so, Canada has barred blood donations by recent visitors to the U.K. And the Food and Drug Administration has recommended that anyone who spent a total of 6 months in Britain between the years 1980 and 1996 refrain from donating; this translates to about 2 percent of the donor population. "More and more people are being told that their blood is 'bouncing' at blood banks," Klein observed.
Creutzfeldt-Jakob disease another illness laid to the mysterious workings of a pathogen called a "prion" doesn't seem to be associated with transfusion, either, Klein stated. CJD, which affects about 1 in 1 million Americans, is screened for, however, using family history information taken at blood banks. Klein cautioned that, since CJD has such a long incubation period as much as 40 or more years it is not currently possible to prove that there is no risk of its transmission via transfusion.
Klein emphasized that with CJD and mad cow disease, the disease risk is purely theoretical; no science suggests they threaten the blood supply. "While we need to remain vigilant and caution is certainly important, we must not make well-intended decisions that have severe implications for the supply of blood. Continually eliminating apparently healthy donors for minimal theoretical safety risks is ill-advised because it jeopardizes supply. Supplies are low across the U.S., as well as in our area. Three weeks ago, a young woman who was bleeding in the operating room at Fairfax Hospital could not get O-negative blood from the regional supplier. Fortunately, NIH had 2 units on its shelf."
NIH'ers are by now used to getting urgent emails from the NIH Blood Bank asking for donations of unusual types, and they are likely to continue. Klein reported that, nationally, red cell collection is down markedly, and that 8.6 percent of U.S. hospitals report canceling surgery for 1 or more days due to lapses in the blood supply.
"We do have to start being seriously concerned about the availability of blood," he said. "(Hospitals) have to have the right (blood) group at the right time."
Klein concluded with a dual message: "Blood is not entirely risk free, but it is very safe." With some 16 million units of blood and blood components transfused annually in the U.S., he explained, "A zero risk is unrealistic. We also need to protect and increase our donor base and frequency."
In cases where you can donate blood for yourself ahead of time, that is to be preferred, he said. But even when circumstances are such that you can't, you are still in pretty good hands.
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