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The Test Sample
What is being tested?
Human T-lymphotropic virus (HTLV) infection 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, rare nervous system disorder, chronic pulmonary infection, uveitis, infectious dermatitis, or other inflammatory disorder.
Two types of HTLV are most commonly identified through testing: HTLV-I and HTLV-II. It is estimated that 15-20 million people worldwide are infected with HTLV. The prevalence of HTLV-1 infection is greatest in Japan, sub-Saharan Africa, the Caribbean islands, and Central and South America. HTLV-II appears to be endemic among Native American populations and is prevalent among intravenous (IV) drug users in North America and Europe.
In the United States, about 22 out of every 100,000 people are infected with HTLV, with HTLV-II infection being more common than HTLV-I infection. HTLV-II infection is associated with female sex, older age, non-white race/ethnicity, lower educational level, and residence in the Western and Southwestern U.S. Some Native American Indian populations have infection rates as high as 13%. Those most likely to be infected with HTLV-I have immigrated to the U.S. from a country where HTLV-1 infection is prevalent, are children of such immigrants, are IV drug users, or are sex workers.
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.
Other risk factors for HTLV infection include: 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; being Native American Indian; or having a history of blood transfusions.
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 Sjögren syndrome
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 from the lower back using a procedure called a lumbar puncture (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.