Patient Test Information

Parvovirus B19

Also known as:

Parvovirus; Parvo B19

Formal name:

Parvovirus B19

Related tests:

Reticulocyte Count

Why Get Tested?

To determine if you have, or recently had, a parvovirus B19 infection if you are at increased risk of complications from this viral infection; if a fetus is at high risk of contracting parvovirus B19 from a mother who is infected or has been exposed

When to Get Tested?

When a pregnant woman has a parvovirus B19 infection or has been exposed to someone with the virus; when someone, especially an immune-compromised person, has persistent or severe anemia

Sample Required?

A blood sample drawn from a vein in your arm for parvovirus B19 antibody testing; to detect the virus itself, the sample tested may be blood or, rarely, bone marrow; in certain cases, fetal cord blood or amniotic fluid may be collected to test for fetal parvovirus B19 infection.

Test Preparation Needed?

None

How is it used?

Parvovirus B19 testing is generally not used to test those with mild and uncomplicated infections. It is typically used to detect a current infection or determine immunity in those who are at an increased risk of complications, such as those with sickle cell anemia. There are several methods of detecting a parvovirus B19 infection:

Antibody testing
Two types of parvovirus B19 antibodies may be produced in response to an infection: IgM and IgG. IgM antibodies are the first to be produced by the body in response to a parvovirus infection. They are present in most individuals within a week or two after the initial exposure. IgM antibody production rises for a short time period and then declines. Eventually, the level of parvovirus IgM antibody usually falls below detectable levels. IgG antibodies are produced by the body a few weeks after the initial infection to provide long-term protection. Levels of IgG rise during the active infection, then stabilize as the parvovirus B19 infection resolves. Once a person has been exposed to parvovirus B19, that person will have some measurable amount of IgG antibody in their blood for the rest of their lifetime.

Parvovirus B19 antibody testing may be performed to determine immunity to parvovirus in pregnant women who have been exposed to someone with parvovirus B19 or who have symptoms suggestive of parvovirus infection. It may also be ordered for people who have acute or chronic anemia or persistent joint pain that may be due to a parvovirus B19 infection. By comparing the absence or presence of both IgG and IgM in the same sample, the health practitioner can distinguish between current, recent, and previous infections. Antibody testing is usually not performed on children who have the characteristic fifth disease rashes and, since parvovirus B19 infection is widespread and causes few problems to those with healthy immune systems, general population screening is rarely done.

Viral detection
Viral detection involves finding parvovirus B19 genetic material (DNA) in a blood sample or, less commonly, in a sample of bone marrow, fetal cord blood, or amniotic fluid. Parvovirus B19 DNA testing is performed primarily to detect active parvovirus infection in immune-compromised people who have acute or persistent anemia. These people will frequently not produce a sufficient amount of antibodies to detect or to resolve the infection. It may also be performed to detect the presence of the virus in babies when a mother is infected or was exposed during the pregnancy.

When is it ordered?

Parvovirus B19 testing is usually not required when a child has the characteristic "slapped cheek" and lacy rashes. The distinctive rashes are sufficient evidence for the health practitioner to be able to diagnose the infection. In general, most people who have or have had parvovirus B19 do not require laboratory testing because illness does not typically last more than 5-7 days and symptoms are usually mild.

Parvovirus B19 IgG and IgM antibody tests may be ordered when a pregnant female has flu-like symptoms and/or has been exposed to someone with a parvovirus B19 infection to determine if she has an active infection, had a recent infection, or has been exposed in the past.  DNA testing may be performed on fetal samples in some cases.

Antibody testing and/or DNA testing may be ordered when someone has acute or persistent anemia or joint pain that the health practitioner suspects may be due to a parvovirus B19 infection. Parvovirus B19 DNA testing is usually ordered when the affected person is immune-compromised.

One or more parvovirus B19 tests may be repeated if they are initially negative but the health practitioner still suspects that a parvovirus infection is present, or to evaluate changes in concentrations of antibody over time.

What does the test result mean?

Antibody testing
If both parvovirus B19 IgG and IgM are present, then it is likely that the person tested has an active, or had a recent, parvovirus infection. This can be confirmed by measuring IgG levels again 2 or 3 weeks later. A high level of IgG is not as important as an increasing concentration of antibody. If there is a 4-fold increase in IgG between the first and second sample, then the person has an active, or had a recent, infection.

If only IgM is present, then the person may have very recently been infected, within the previous 2-4 months. If only parvovirus B19 IgG is present, then the person had a parvovirus infection at some time in the past and has protection against the virus.

If antibody tests are negative, then the person tested has not had the infection and is not immune. If a pregnant woman is not immune and has been exposed to someone with the disease, she will typically be closely monitored by her doctor.

If someone is symptomatic but has low or undetectable levels of IgG and/or IgM, it may mean that the person either has a condition other than parvovirus B19 or that their immune system is not responding normally. i.e., not producing an adequate amount of antibody even if parvovirus is present. This may be true for immunocompromised people and DNA testing may need to be done.

Viral detection
If a parvovirus B19 DNA test is positive, then the person is currently infected with parvovirus B19. A negative result does not rule out the infection. The virus may not be present in sufficient amount in the sample to be detected.

Fetal infection of parvovirus B19 is often detected through testing of viral DNA in maternal samples as well as samples from the baby.

The PCR assay is used to detect viral DNA and is the optimal method for detecting chronic infection in immunocompromised patients as the antibody levels are variable.

Is there anything else I should know?

Sometimes a reticulocyte test may be performed along with parvovirus B19 testing to evaluate red blood cell (RBC) production. This test measures new immature RBCs, called reticulocytes, in the blood that still contain genetic material. Since parvovirus B19 disrupts RBC production, the number of reticulocytes will decrease during an active infection.

Parvovirus B19 infections are usually self-limiting (limited in duration) in otherwise healthy people. Treatment may be given to relieve symptoms and, when necessary, to address anemia.

A pregnant woman who passes parvovirus B19 infection to her fetus will be closely monitored for several weeks with periodic ultrasounds. In most cases, the fetus will be healthy. When hydrops fetalis or severe anemia develops, it can sometimes be addressed by giving the fetus a blood transfusion. The parvovirus B19 infection is not known to cause birth defects.

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.

  1. Is this the same parvovirus that affects dogs and cats? Can I catch it from my pet?

    No. Different types of parvovirus infect humans and animals. You cannot get parvovirus from your pets, and they cannot catch it from you.

  2. Is there any way to prevent getting a parvovirus B19 infection?

    There is no vaccine available for parvovirus. The virus is passed through close contact, and people may be infectious even when no symptoms are present. However, careful hygiene, such as diligently washing hands and covering the mouth and nose when coughing or sneezing, can help prevent transmission of the virus. Most people are infected when they are children.

  3. Can my test be performed in my doctor's office?

    No, parvovirus B19 testing requires specialized equipment to perform. Your sample will usually be sent to a reference laboratory.