HTLV (human T-cell lymphotrophic virus) is a virus that particularly infects T-cells (a category of white blood cells involved in immune response). There are two subtypes of HTLV: HTLV-I and HTLV-II. The test detects antibodies produced by the body in response to infection by either of the two subtypes of HTLV.
More than 95% of individuals infected with HTLV will never show symptoms, but they can re-transmit the virus to other people (sexual relations, needle sharing, transfer from mother to baby during delivery or breastfeeding, etc.). The virus remains dormant in the body permanently, but can reactivate and cause disease (leukemia or T-cell lymphoma), nerve damage resembling multiple sclerosis, inflammation of the eye (uveitis) or joints, and other autoimmune inflammatory diseases.
A negative (non-reactive) result indicates that HTLV is probably not responsible for the reported symptoms. A positive (reactive) result must be confirmed by a more precise technique to rule out a false positive result. An unclear test result must be repeated several weeks later and a negative or unclear result at that time indicates that HTLV is probably not involved.