What Does A Positive Parvovirus B19 IgG Mean & How Long Does Parvovirus IgM Stay Positive?

Positive IgG is thought to be protective and is associated with a minimum risk of parvovirus B19 infection.(1)

Positive IgM is indicative of recent infection.(1)

What Does Positive Parvovirus B19 IgG Mean?

Both IgG and IgM are found in the serum at or soon after the onset of illness and reach their maximum levels within 30 days of the illness. The presence of IgG antibodies indicates past exposure/infection; whereas the presence of IgM antibodies indicates current/recent infection. IgG is also considered to be protective as it reduces or minimizes the chance of new B19 infection since antibodies against parvovirus are already present in the serum, which will fight off invading parvovirus B19.

Since IgG antibodies remain in the serum for years, the diagnosis of recent or acute infection is made based on the presence of IgM antibodies. There is an increased prevalence of B19 IgG antibodies with increasing age. In children <5 years the prevalence is around 2-9%, in children aged 5-18 years the prevalence is around 15-35%; whereas in adults ≥19 years the prevalence is greatest around 30-60% (1).
Since the presence of IgM B19 antibodies indicates current or a recent infection it is only detectable for months in the sera; whereas, IgG B19 antibodies are detectable throughout life.(2)

Interpretation of positive/negative IgG and IgM antibodies in parvovirus B19 infection is given in the table given below(1):

Parvovirus IgG resultParvovirus IgM ResultInterpretation
IgG negativeIgM negativeNo history of past infection. Increased susceptibility to parvovirus B19 infection.
IgG positiveIgM negativeHistory of past infection. Minimal risk of parvovirus B19 infection.
IgG positive or negativeIgM equivocalIndicative of current or recent infection. Retesting should be done in 1-2 weeks.
IgG positiveIgM positiveIndicative of current or recent infection.
IgG negative or equivocalIgM positiveIndicative of recent infection. Retest in 1-2 weeks.

How Long Does Parvovirus IgM Stay Positive?

In most of the B19V infection cases, there is no need for laboratory testing as the symptoms are mild and the infection resolves within 5-7 days. Serological tests of parvovirus B19 that includes anti-parvovirus B19 IgG and IgM antibodies are done with enzyme-linked immunoassay (ELISA), immunofluorescence, and radioimmunoassay. The interpretation of IgM results becomes difficult due to a lack of laboratory standardization and an increase in false-negative test results of IgM. Therefore, polymerase chain reaction (PCR) for detecting B19 DNA is chosen over serological tests. However, the definitive diagnosis of acute or chronic infection is made based on both PCR and serological testing.

Interpretation Of Serological Testing In Pregnant Women

In pregnant women who are exposed to parvovirus B19, serological testing of IgG and IgM should be carried out immediately. If IgG is positive and IgM negative then there is no risk to the fetus as the mother was infected by B19 in the past with no recent infection and already has B19 antibodies present in the sera. If both IgG and IgM are positive, then this indicates recent infection within 7-120 days and the fetus is at risk of B19 transmission. If IgG results are negative with positive IgM results then that indicates acute infection with no previous antibodies against B19 and the fetus is at greater risk as the mother is not immune. If both IgG and IgM are negative, then it indicates that the mother is not immune and there is no evidence of an acute infection. In this case, re-testing should be done in 3 weeks. Acute infection is suspected if IgM is positive in subsequent testing.(2)

Parvovirus B19 is the only virus of the Parvoviridae family that is infectious to humans. It is a very common infection that is found in children and transmitted to adults. By age 30, about 60% of adults develop seropositivity from 5-10% in children aged 2-5 years. The most common disease associated with parvovirus is erythema infectiosum that mostly causes rashes in children and associated acute symmetric arthritis in adults. It also precipitates anemias in patients with blood disorders or immunosuppression.(2)

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