Human T-cell Lymphotropic Virus (HTLV) Testing

Human T-lymphotropic virus (HTLV) testing is used to detect an infection by HTLV-I or HTLV-II. When the virus enters the body, it preferentially infects T-cell lymphocytes. The body's immune system responds by producing antibodies that target the virus. Most individuals who are infected do not develop an active illness, but a rare few will develop a condition related to a disorder of the T-cells.

HTLV testing may be used in a few different ways:

• In people with risk factors for HTLV (such as living in parts of the world where HTLV infection is more common, having a sexual partner who came from one of these areas, having multiple sex partners, being an IV drug user, being a Native American Indian, or having a history of blood transfusions), testing may be used to follow-up abnormal findings from a complete blood count (CBC) and WBC differential, such as an increased number of immature and/or abnormal lymphocytes.
• To diagnose the cause of a T-cell-related disorder if a person has symptoms consistent with HTLV-I–associated myelopathy/tropical spastic paraparesis (HAM/TSP), especially if the person has risk factors associated with this condition; in some cases, cerebrospinal fluid (CSF) may be tested for HTLV.
• To determine the source of an affected individual's infection; since HTLV can be passed from mother to baby during pregnancy, the mother of an affected child may be tested for HTLV-I or HTLV-II to determine if she is the likely source of the child's infection. Likewise, the sexual partner of an affected person may be tested.

Two types of HTLV testing are available, antibody and molecular testing:

• Typically, an EIA (enzyme immunoassay) test method is used initially to detect HTLV-I and HTLV-II antibodies in the blood. If the initial test is positive, a second method, such as Western blot, is ordered to confirm the finding and to help distinguish between HTLV-I and HTLV-II.
• In cases where HTLV-I and HTLV-II cannot be distinguished, molecular testing (polymerase chain reaction method, PCR) that detects the genetic material of the virus may be performed.

In the U.S., all donated blood is screened for HTLV. If a person who has donated blood tests positive for HTLV-I/II, then confirmatory testing may be performed to determine if the initial screening result is a false positive or if the person who donated the blood has an HTLV-I/II infection.

HTLV testing may be performed when a person has symptoms or findings that suggest that the person has a condition associated with an HTLV-I or HTLV-II infection, especially when that person also has identified risk factors.

Signs and symptoms of adult T-cell lymphocytic leukemia or lymphoma may include:

• Fever
• Night sweats
• Fatigue
• Increased number and abnormal immature lymphocytes
• Enlarged lymph nodes

Symptoms of HTLV-I–associated myelopathy/tropical spastic paraparesis (HAM/TSP) may include:

• Weakness in the lower limbs
• Muscle spasms and contractions
• Lower back pain
• Muscle stiffness
• Urinary, bowel, and sexual dysfunction

Testing may be performed on:

• A mother when her child has been diagnosed with an HTLV infection
• The sexual partner(s) of a person when that person has been diagnosed with an HTLV infection
• A person when he or she has been told that the blood that the person donated was positive for HTLV-I/II
• A person when he or she has risk factors and symptoms that the healthcare practitioner suspects may be linked to an HTLV infection, such as uveitis, dermatitis, or arthritis

HTLV testing is usually done in a stepwise fashion and usually includes an initial test followed by confirmatory testing, depending on the results.

If initial HTLV testing is negative, then it is unlikely that the individual has an HTLV infection and the person's symptoms are likely due to another cause. Typically, no further testing is necessary.

If someone has HTLV-I or HTLV-II antibodies on both initial and confirmatory testing, then it is likely that the person has an HTLV infection. If the person also have symptoms linked to an HTLV-associated condition, then it is likely that this infection is the underlying cause.

A person with positive initial and confirmatory results but no symptoms, such as someone who has been tested because she is the mother of an affected child or the sexual partner of an affected person, or someone whose donated blood was positive and confirmatory testing is also positive, is likely to have the infection. However, in the vast majority of cases, the person will never develop an illness. These people can, however, pass the infection on to other people and should take necessary precautions (see Common Questions #3).

Those who have a positive initial HTLV-I/II test and a negative confirmatory test likely have a false positive and not an HTLV infection. Those with an indeterminate confirmatory test result should be retested in several weeks to determine if they have developed antibodies. If the confirmatory testing is negative or still indeterminate, then it is unlikely that the person has an HTLV infection.

A positive HTLV-I/II molecular test indicates that the person tested has an HTLV-I or HTLV-II infection. If the molecular result is negative, then the person is less likely to be infected, but it cannot be ruled out as the amount of virus in the blood may have been too low to detect at the time of the test.

The following table summarizes some typical results that may be seen with HTLV testing:

The HTLV-I/II viruses become inactive (latent) in the body after an infection, but they are never totally eradicated. For this reason, a person who has tested positive will not be able to donate blood.

HTLV-II antibodies may show a positive result on a test for HTLV-I antibodies (cross-reaction). This means that even though a person has really had an HTLV-II infection, initial testing may show an HTLV-I positive test result.

No. The incidence of HTLV-I/ll is low in the United States and most people who are infected do not ever become ill, so it is not considered necessary. However, since the viruses can be passed from one person to another through blood transfusions and organ transplants, all donated blood (since 1988) and all relevant donated organs are tested for HTLV-I/II.