Transmission of the retroviruses human T-lymphotropic virus types I and II (HTLV-I/II) require cell-to-cell contact—mother to child transmission, sexual transmission, and transmission via transfusion have all been documented. HTLV can be asymptomatic for decades. However, HTLV-I infection has been associated with adult T-cell leukemia/lymphoma (ATL), HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP), and HTLV-associated uveitis; and HTLV-II has been linked to hairy cell leukemia. Serological screening tests for HTLV-I and HTLV-II have been recommended for donated blood since 1988 and 1998, respectively. The serological tests, however, have a high false-positive rate; ~5% of donations with reactive screening tests are confirmed positive after retesting. The final guidance provides recommendations for donor reentry; donors may be reconsidered for reentry if one of two screening tests was indeterminate, negative, or not performed. For a donor to reenter, a sample must be collected and screened with two tests at least 6 months after the deferral date; if both screening tests are negative, the donor may be reentered. If one of the screening tests is positive or indeterminate, the donor must be deferred permanently. If the donor tests reactive on one test and non-reactive on the second test, the donor must remain deferred but is eligible for one more follow-up. Many deferred donors with unconfirmed HTLV screening tests could potentially be requalified with this final FDA guidance.
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