Blood screens may need a finer mesh.

Current screening methods for donated blood in the United States may miss fragments of a virus that is linked to a form of leukemia, new research shows.

Blood from donors is routinely screened for antibodies that signal the presence of human T cell lymphotropic virus (HTLV), which can cause T cell leukemia. Researchers at New York University Medical Center have now found, however, that some people who do not have such antibodies may nevertheless harbor fragments of HTLV.

The team tested blood samples from 81 former intravenous drug users who were HIV-negative. Drug users have high HTLV infection rates, so the researchers figured they would need relatively few blood samples to compare techniques. Routine tests used to screen donated blood revealed that 18 of the volunteers had antibodies to HTLV. Specialized tests that are sensitive to the presence of the virus itself showed that 39 had partial sequences of HTLV DNA. In all, 42 volunteers tested positive for HTLV in one or both analyses.

Thus, HTLV may be more widespread than currently believed, report Dorothea Zucker-Franklin and her colleagues in the June 10 Proceedings of the National Academy of Sciences. Although rates of infection would be much lower in the general population than they are among former drug users, the research raises troubling questions, she says.

Scientists don't know whether just having these fragments in the blood can lead to infection by HTLV, Zucker-Franklin says. The researchers became curious about these viral fragments after finding them in people who have mycosis fungoides--a rare skin cancer resulting from a T cell lymphoma. In this disease, malignant cells apparently reach the skin by circulating in the blood. Standard blood tests show that people with mycosis fungoides usually do not carry antibodies to HTLV.

The researchers wondered whether healthy people without the cancer might also carry viral fragments that could slip through the screen. They tested the blood of healthy individuals who were related to people with mycosis fungoides, using both routine and specialized screenings. Standard blood screening found no HTLV antibodies in the group, but in further testing six of the eight relatives tested positive for HTLV fragments. Apparently, people can carry fragments of the virus without developing mycosis fungoides or leukemia, says Zucker-Franklin.

The Food and Drug Administration is now considering whether to require tests for both HTLV fragments and antibodies.