BLOOD donors in the US will soon be given a controversial new HIV test when they give blood. The test improves the odds of detecting donors with HIV, but critics claim that it costs so much – and prevents so few additional infections – that it is a waste of money that could be put to better use.
“Medical care is under enormous fiscal pressure, yet here we are throwing what seems to me an inappropriate amount of resource to prevent a minuscule number of infections,” says Michael Busch, a virologist specialising in transfusion medicine at the University of California at San Francisco.
At present, blood banks test for the presence of antibodies against HIV in every unit of blood they collect. This reliably detects individuals with well-established HIV infections, and their blood is then discarded. However, people who have only recently become infected with HIV pass through a “window phase”, estimated to last between 11 and 22 days, during which they have not yet developed detectable levels of antibodies but can still transmit the virus through their blood. Every year, blood collected from people during this window phase causes about 30 to 40 new HIV infections in transfusion patients in the US.
The new test partially closes this window by testing directly for a protein, or antigen, called p24 on the virus itself. HIV antigen becomes common enough to detect in the blood about a week before anti-HIV antibodies do. The test should detect about ten units of infected blood each year that would otherwise have gone to unlucky transfusion patients.
The US Food and Drug Administration is expected to approve the test early this year. The FDA has already issued a memo advising blood banks that they must begin to use the test within three months of its approval.
The new test will have to be used in conjunction with the present one because once the infection has progressed beyond the window phase and antibodies have developed, very little free virus remains in the bloodstream, and the test for HIV antigen often fails to detect it. The new test will cost between $40 million and $100 million pet year, or as much as $10 million per infection prevented, says Busch.
But this underestimates the true cost, he says. Most units of transfused blood go to people so ill that they die without ever leaving the hospital, and many of the rest go to people who live only a few more years. Busch reasons that none of these people will benefit from the extra screening, because even if they are infected it takes an average of ten years to develop clinical AIDS. Taking this into account, he calculates that HIV antigen screening will cost $2.2 million per year of life saved. By contrast, HIV antibody testing costs only $5000 per year of life saved, and even such a heroic measure as a heart transplant costs only $30 000 per year of life saved.
“The general rule in public health today is that anything that costs more than $50 000 per life-year saved is not cost-effective,” says Busch. The health care system would get more for its money elsewhere. For example, the $100 million that HIV antigen testing might cost is roughly equivalent to the US Centers for Disease Control’s entire budget for AIDS prevention programmes, which clearly prevent more infections, he says.
Last summer, the FDA’s Blood Products Advisory Committee voted against insisting that blood banks use the test. After pressure from the public and Congress, however, the agency overruled its advisers. “Our role is to protect the public’s health. We’re not supposed to consider the cost,” says Lorrie Harrison, a spokesperson for the FDA.