Blood lines: Screening for infectious agents is bleeding reserves dry, experts warn

Emerging infections such as West Nile virus, mad cow disease and foot-and-mouth disease are shrinking the global blood supply, which was already threatened by the AIDS epidemic. The dwindling reserves, say experts, could spell doom for hospitals worldwide.

US blood banks have enough blood to meet demands for roughly two or three days. But a five-to-seven day margin is optimal, says Roger Dodd, president of the American Association of Blood Banks. Worldwide, the picture is equally grim: there are about 75 million blood collections every year, but the majority of the world's population has access to only 40% of the available blood. The reserves are also falling because of a shifting demographic, adds Dodd. “People seem less and less inclined to give blood,” he says.

For years, scientists have been trying to create viable blood substitutes, but that goal has been elusive. Two US products are now close to reaching the clinic: Hemopure, made by Cambridge-based Biopure, and PolyHeme, developed by Northfield Laboratories of Illinois. Neither can replace blood entirely—most substitutes focus primarily on transporting oxygen—but will at least serve as a “bridge” in emergency situations, their makers say.

Hemopure, made from purified bovine blood, is farthest along in the regulatory process. Already approved in South Africa, it delivers oxygen three times more efficiently than red blood cells and can be administered regardless of blood type, says Biopure spokesman Douglas Sayles. Hemopure also has a three-year shelf life—much longer than the 42-day life span of red blood cells.

Once inside a patient however, Hemopure lasts only for 12–24 hours, whereas transfused red blood cells can live for up to 50 days. Scientists remain skeptical about blood substitutes for that reason, calling them a short-term solution useful only for specific indications such as military operations and heavy trauma episodes, where physicians need blood quickly.

Creating substitutes for blood is challenging because of the multitasking nature of the viscous life force: blood carries oxygen, nutrients and waste products, and helps repair injuries. Most substitutes are derived from oxygen-carrying perfluorocarbons or natural hemoglobin. But Fluosol, the only blood substitute ever approved by the US Food and Drug Administration (FDA), was taken off the market because patients given Fluosol breathed pure oxygen—which can be toxic.

Hemoglobin-based substitutes stem from outdated human blood, cow blood or recombinant hemoglobin produced by bacterial cells. Recently, the common marine worm was suggested as another promising alternative. But hemoglobin-based substitutes also carry the risk of toxic side effects, such as inflammation and oxygen stress.

Some researchers are trying to grow blood vessels in a test tube. A Harvard University research team also recently reported that adding uridine diphosphate-galactose to blood platelet cells increases their shelf life from 5 days to 12 (Science 301, 1531–1534; 2003)

The real test for any substitute, says Tom Moore, chief executive officer of Biopure, is getting FDA approval. “It is a challenge to run a clinical trial against a natural product,” Moore says. “Blood has never really been characterized, so the standards we are putting ourselves against are murky.”