The Test Sample
What is being tested?
Parvovirus B19 is a virus that causes a common childhood illness, also called "fifth disease" or "erythema infectiosum." The virus is found in respiratory droplets during an infection and is easily transmitted to others through close physical contact. Parvovirus can also be passed from a pregnant woman to her fetus and transmitted through exposure to blood and blood products.
In the United States, as many as 50% of adults and 85% of the elderly have been infected with parvovirus B19, usually as children or young adults. The infection typically has an incubation period of several days to 2-3 weeks, is active for a short period, and then begins to resolve.
For most people, parvovirus B19 infection is indistinguishable from other mild illnesses that develop and go away within a short time period. Many who are infected have no symptoms or have mild flu-like symptoms such as fatigue, a slight fever, headache, or an upset stomach, and many may not know that they have had a parvovirus B19 infection. The majority of people do not experience any significant symptoms or health problems and once the initial infection resolves, the person becomes immune and will not get the infection again.
Some children with the infection develop a characteristic and distinctive bright red "slapped-cheek" rash on both cheeks and a raised lacy rash on the torso and extremities. The rashes may come and go for several weeks, reappearing and/or intensifying with exposure to heat and sunlight and with stress. By the time the rash appears, the child is no longer considered infectious. Parvovirus is sometimes called fifth disease because it is the fifth of six common childhood illnesses that can cause rashes.
Less commonly, some adults become infected and may develop "gloves and socks syndrome" with painful swelling of joints and reddening of the hands and feet that typically ends abruptly at the wrists and ankles. This condition usually resolves within a few weeks. Symptoms of arthritis may also occur in adults and children, but like "gloves and socks syndrome," tends to resolve a few weeks after infection. Some severe cases, however, have been tied to chronic arthritis and even to the development of rheumatoid arthritis.
Parvovirus B19 can cause major health problems in three types of patients:
- People with iron deficiency anemia or a condition that affects or shortens the life of red blood cells (RBCs), such as sickle cell anemia or thalassemia, may develop severe acute anemia during a parvovirus B19 infection. Parvovirus B19 targets cells in the bone marrow that become RBCs and disrupts the production of new RBCs, which can more severely affect those with underlying blood disorders.
- Women who are infected during pregnancy can pass the infection to their babies. Most fetuses will be fine, but a small percentage will develop severe anemia and a few may have an inflammation and infection of the heart muscle (myocarditis). These conditions can cause miscarriage, congestive heart failure in the fetus, hydrops fetalis (associated with fluid accumulation), and sometimes stillbirth. The greatest risk for fetal complications is during the second trimester of pregnancy.
- In those with compromised immune systems, a parvovirus B19 infection may cause chronic anemia and be challenging to resolve. This includes people with HIV/AIDS, those who have had organ or bone marrow transplants, and those undergoing chemotherapy treatment for cancer.
Parvovirus B19 testing is not typically used to screen the general population and is not deemed necessary in most cases of infection because symptoms are mild and time-limited. It is usually ordered to determine whether someone is currently, or has recently been, infected with parvovirus only if they are at risk of complications. It may also sometimes be ordered to determine whether someone has ever been exposed to parvovirus. Testing involves either a measurement of parvovirus antibodies—immune proteins produced in response to parvovirus B19 exposure—or the detection of the genetic material of the virus itself (its DNA) during an active infection.
How is the sample collected for testing?
The sample required depends on whether testing is being done to determine the presence of antibody or to detect the virus itself as well as on the health status of the patient. Antibody testing requires a blood sample, obtained by inserting a needle into a vein in the arm. Viral detection may be done on blood or, more rarely, on a sample of bone marrow collected through a bone marrow aspiration or biopsy.
In the case of a pregnant woman at risk of passing infection to her baby, fetal cord blood or amniotic fluid may be collected for testing. Fetal cord blood is obtained by guiding a needle into the vein of the umbilical cord with the assistance of ultrasound imaging. Amniotic fluid is obtained through amniocentesis, or inserting a needle into the amniotic sac surrounding the fetus and removing a small sample.
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.