NEW YORK — Ever since scientists first linked an obscure blood-borne virus to chronic fatigue syndrome two years ago, blood centers around the world have been scrambling to determine whether their collections are safe. With memories of previous blood scares still fresh in the minds of blood bank officials, many collection centers have even gone so far as to bar donations from people with the disease. But it's not just xenotropic murine leukemia virus–related virus (XMRV) that threatens global blood supplies today. Even well-known pathogens such as hepatitis B virus can slip through the cracks of existing screening techniques, leading to contaminated blood products and accidental infections.

Newly implemented technologies might change all that. Speaking at the New York Academy of Sciences here in late March, a panel of blood bank officials and infectious disease experts unveiled plans to make blood supplies safer by introducing DNA-based screening tests to improve disease detection.

“Our blood supply is safer than it's ever been,” Gail Moskowitz, a healthcare consultant who has directed several blood banks in the New York area, said at the 29 March meeting. “But transfusion is still associated with [a] risk of transmission.”

In most blood banks across the developed world, each unit of blood is screened for a panel of infectious agents, including HIV, hepatitis B and C viruses, leukemia-associated human T-lymphotrophic virus and the syphilis-causing bacterium. Existing serological assays reveal most pathogens in the blood supply. Yet many of the commonly used tests rely on finding antibodies or pathogens circulating in people's blood and can fail in rare cases when recently infected donors have not yet mounted large immune responses or when viral counts remain low.

A closer look: Pathogens can go undetected. Credit: istockphoto

Aiming to boost pathogen detection rates, over the past decade or so blood banks in the US have introduced new PCR-based techniques that can pick up minute levels of HIV and hepatitis viral RNA in the bloodstream—and the approach seems to have paid off. Reporting in February, a team led by Susan Stramer, executive scientific officer of the American Red Cross in Gaithersburg, Maryland, found that, among close to 4 million blood samples analyzed, a DNA-based assay was more effective than conventional tests at detecting these three viruses in newly infected donors, including those previously vaccinated against hepatitis B (N. Engl. J. Med. 364, 236–247, 2011). Looking beyond HIV and hepatitis, at the March meeting Stramer also reported the results of a 5,000-donor study from Puerto Rico demonstrating that a similar genetic test was ten times more sensitive in detecting Dengue virus than conventional blood assays.

It's not just viruses that pose a problem, either. The parasites responsible for malaria and babesiosis remain serious safety concerns, but as yet no lab test is licensed to screen blood for the protozoans that cause either disease. Also at the meeting, Sanjai Kumar, who heads the Laboratory of Emerging Pathogens at the US Food and Drug Administration in Rockville, Maryland, reported unpublished data showing that DNA-based tests for both diseases can identify as few as two parasites per milliliter of blood—a detection rate greater than 1,000 times more sensitive than conventional microscopy-based testing.

Yet, even though genetic testing is making the blood supply safer, Stramer notes that price remains an obstacle to implementing the advanced screening techniques. “We are in a technology stranglehold,” she says. “Even if a technology can be developed, who is going to pay for it? Hospitals don't want to pay more for blood.”