Patient Test Information


Also known as:

Human T-cell Lymphotropic Virus; HTLV-I/II Antibodies; HTLV-I/II by PCR

Formal name:

Human T-Lymphotropic Virus Types I/II Antibodies; Human T-cell Lymphotropic Virus Types I/II by PCR

Related tests:

Complete Blood Count, WBC Differential, Immunophenotyping, Bone Marrow Aspiration and Biopsy

Why Get Tested?

To detect a human T-lymphotropic virus (HTLV) infection; to help diagnose the cause of adult T-cell leukemia or lymphoma or HTLV-associated myelopathy

When to Get Tested?

When you have signs or symptoms that suggest that you may have an HTLV-associated condition, especially when you have identified risk factors; rarely when you have donated blood and been told that you are positive for HTLV

Sample Required?

A blood sample drawn from a vein in your arm; rarely a sample of cerebrospinal fluid (CSF) collected by a doctor from the lower back using a procedure called a lumbar puncture or spinal tap

Test Preparation Needed?


How is it used?

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, or having a history of blood transfusions, testing may be used to follow-up abnormal findings from a CBC (Complete Blood Count) 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, 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 that detects the genetic material of the virus (polymerase chain reaction method, PCR) 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.

When is it ordered?

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

symptoms and signs 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 a 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 they have been told that the blood that they donated was positive for HTLV-I/II
  • A person when they have risk factors and symptoms that the doctor suspects may be linked to an HTLV infection such as uveitis, dermatitis, or arthritis

What does the test result mean?

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 they are 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, they will never develop an illness. These people can, however, pass the infection on to other people and should take necessary precautions.

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 a 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:

Initial Antibody Testing (HTLV I/II) Confirmatory Testing (Western blot) Additional Testing Likely Interpretation
Negative N/A N/A No infection
Positive Negative Repeat Western blot negative False positive on initial test
Positive Positive HTLV-I N/A HTLV-I infection
Positive Positive HTLV-II N/A HTLV-II infection
Positive Indeterminate Molecular test (PCR) positive or repeat Western blot positive for HTLV-I or HTLV-II HTLV-I or HTLV-II infection
Positive Indeterminate Molecular test (PCR) negative or indeterminate and repeat Western blot negative or still indeterminate Likely false positive on initial antibody testing

Is there anything else I should know?

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, their initial testing may show an HTLV-I positive test result.

What is being tested?

Human T-lymphotropic virus (HTLV) is associated with certain rare diseases of T lymphocytes (T-cells), a type of white blood cell that is an important part of the body's immune system. This test detects an HTLV infection in order to help identify the virus as the underlying cause of an individual's leukemia, lymphoma, or rare nervous system disorder.

Two types of HTLV are most commonly tested: HTLV-I and HTLV-II. It is estimated that 15-20 million people worldwide are infected with HTLV. There is a higher incidence of HTLV-I in areas near the equator, in the Caribbean, parts of Africa, southwestern Japan, and southeastern United States. A higher incidence of HTLV-II is found in Native American populations and in North American and European intravenous (IV) drug users.

An HTLV-I infection can be passed from mother to child during pregnancy or breastfeeding. Both HTLV-I and HTLV-II infections can be sexually transmitted or spread through exposure to contaminated blood as occurs with sharing of needles during IV drug use, although the majority of drug use-related infections are linked to HTLV-II. Both types may be passed through a blood transfusion or an organ transplant, but infection due to these procedures is now rare in the United States because all donors are tested for HTLV-I/II.

Living in parts of the world where HTLV is more common (such as those listed above), having a sexual partner who came from one of these areas, having multiple sex partners, being an IV drug user, or having a history of blood transfusions are all factors that increase an individual's risk for HTLV infection.

Both HTLV-I and HTLV-II preferentially infect T-lymphocytes. Most people infected with HTLV-I or HTLV-II will have few to no symptoms but can pass the infection on to others. After the initial infection, the virus never completely goes away but remains in the body in an inactive (latent) form. A small percentage of those infected go on to develop one of several associated diseases, typically months to many years or even decades after their initial exposure, and may then become acutely or chronically ill.

HTLV-I is associated with:

  • Adult T-cell leukemia/lymphoma (ATL), a type of white blood cell cancer that may progress rapidly or slowly and cause symptoms such as fatigue, fever, and enlarged lymph nodes
  • HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a rare condition that can cause weakness in the lower limbs, muscle spasms, nerve pain, and urinary incontinence
  • In some cases, other conditions such as uveitis, HTLV-I-associated infective dermatitis, rheumatoid arthritis, and Sjogren syndrome

HTLV-II is less clearly linked with specific diseases but may be associated with certain lung conditions, neurological disorders, and dermatitis.

The body responds to an HTLV-I or HTLV-II infection by producing antibodies. These antibodies can be detected in the blood during testing. The viruses may also be directly tested using molecular tests (polymerase chain reaction, PCR) that detect the genetic material of the viruses.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm. Rarely, a sample of cerebrospinal fluid (CSF) is collected by a doctor from the lower back using a procedure called a lumbar puncture or spinal tap.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

  1. Should everyone be tested for HTLV-I/II?

    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.

  2. Should I be tested for HTLV-I/II if I have some of the risk factors?

    This would be something to discuss with your health practitioner. If you have risk factors such as you have lived in one of the countries where these infections are more common, have had multiple sex partners, and/or have been an IV drug user, then you and your health care provider may want to consider it.

  3. I found out I am positive for HTLV. What precautions should I take to avoid infecting others?

    You can take several steps to avoid spreading the infection, according to the Centers for Disease Control and Prevention:

    • Tell your health care provider that you have been infected; he or she can speak with you about necessary precautions.
    • Do not donate blood, tissues, organs, or sperm.
    • If you are a new mother, do not breastfeed.
    • Do not share needles or syringes.
    • Use condoms to prevent sexual transmission.
  4. Can I get HTLV-I/II from donating blood?

    No, blood collection is performed using a sterile needle. You cannot get an HTLV infection from donating.

  5. The names HTLV and HIV look and sound similar - are these diseases related?

    They are both retroviruses and can be passed through blood and sexual contact, but they are only very remotely related, and HTLV does NOT cause AIDS and does not have the same devastating effects on a person's immune system that HIV does.

    HTLV and HIV do, however, share a historical naming convention. HTLV-III was the name given to HIV (human immunodeficiency virus) when it was first identified. The virus was later reclassified and the name was changed to HIV. Since that time, the term HTLV-III has been re-used to designate a different HTLV virus. The newly designated HTLV-III virus, as well as an HTLV-IV virus, have been identified and are being studied, but testing of them is only being done on a research basis.