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MoonDragon's Lab Tests & Information
RUBELLA ANTIBODY TITER
IMMUNITY TO RUBELLA (GERMAN MEASLES)
Rubella is caused by a virus that is passed from person-to-person by coughs or sneezes. Any contact with the nasal or throat secretions of an infected person can spread the virus. Women, who have either had the Rubella infection or have received the vaccination, produce an antibody (protein made in response to a foreign substance introduced into the body) in their blood that will usually prevent them from getting the infection a second time. This antibody also protects the unborn baby against the virus; this protection is called immunity.
Rubella infections during childhood usually cause mild symptoms. However, if a woman becomes infected with Rubella during the first three months of her pregnancy and does not have immunity to the virus, the baby is at risk of having serious birth defects or dying.
All women considering a first time pregnancy, or those who are pregnant for the first time, should be tested to see if they have this immunity. A blood specimen is tested to see if a sufficient amount of antibody is present in the blood to protect the mother and the baby. If a woman does not have enough antibodies, she may be given a Rubella vaccination, which will cause her to produce these protective antibodies.
RUBELLA: THE TEST
Also known as: German measles; 3-day measles
Formal name: Rubella antibodies, IgM and IgG
Related tests: TORCH; Antibody tests
TEST PURPOSE
The test is given to evaluate whether a woman is immune to rubella (German measles) as a result of childhood exposure or immunization, or whether she may be presently infected with the disease. The question of a current infection is particularly urgent for pregnant women. Although the disease itself is not serious in adults, it can cause miscarriage, stillbirth, or damage to the fetus during the first trimester (three months) of pregnancy. The rubella test is regarded as a more reliable indication of the patient's immune status than her history, because reinfection with rubella is possible even after immunization. The results of the test may influence decisions to terminate a pregnancy.
The rubella test is used to:
- Confirm the presence of adequate protection against the rubella virus.
- Detect a recent or past infection.
- Identify those who have never been exposed to the virus and those who have not been vaccinated.
- Verify that all pregnant women and those planning to become pregnant have a sufficient amount (titer) of rubella antibodies to protect them from infection.
Both the IgM and IgG antibody tests may be ordered on a person, pregnant or not, who has symptoms that the health care provider suspects are due to a rubella infection. They may also be ordered on a newborn that is suspected to have become infected during pregnancy or that presents with congenital birth defects that the practitioner suspects may be due to a rubella infection.
TEST DESCRIPTION
The rubella test belongs to a category of blood tests called hemagglutination inhibition (HI) tests. Hemagglutination refers to the clumping or clustering of red blood cells caused by a disease antibody, virus, or certain other substances. Inhibition refers to interference with the clumping process. The presence of rubella antibodies inhibits the cell clumping caused by the rubella virus. Thus, the addition of the virus to a sample of the patient's blood allows a doctor to determine the presence and concentration of rubella antibodies and the patient's immunity to the disease.
When a person is infected with the rubella virus, the body produces both immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies to fight the infection. Once IgG exists, it persists for a lifetime, but the special IgM antibody usually wanes over six months. The rubella test can either confirm that a recent infection has occurred (both IgG and IgM are present) or that a patient has immunity to rubella (IgG only is present).
When the test is performed to confirm the diagnosis of rubella in a woman already pregnant, two blood samples are drawn. One is drawn during the acute phase of the illness about three days after the rash breaks out, and the second is drawn during the convalescent phase about three weeks later. The specimens are then tested simultaneously by a single laboratory. Alternatively, a pregnant woman with a rash suspected to be rubella can be tested for IgM antibody. If the test shows that IgM antibody is present, then a recent rubella infection has occurred.
Because there have been cases of children born with rubella syndrome even though the mother's blood test indicated that she was sufficiently immune to rubella, some researchers are presently recommending a second test, known as a synthetic peptide enzyme-linked immunosorbent assay (ELISA). This test screens for the presence of rubella virus neutralizing (RVN) antibodies in the mother's blood.
ORDERING THE TEST
The IgG rubella test is ordered when you are pregnant, planning on becoming pregnant, or whenever a check of immunity against rubella is required. IgM and IgG rubella tests are ordered when a pregnant woman has a fever and rash and/or other symptoms that may indicate a rubella infection. Since many conditions can cause similar symptoms, the health care provider will need to order the tests in order to confirm the diagnosis.
IgM and IgG tests may be ordered on a newborn when the mother was diagnosed with a rubella infection during pregnancy and/or when a newborn is born with birth defects (hearing loss, cardiovascular abnormalities, cataracts, central nervous system disease) that could be due to CRS.
Since IgM and IgG rubella antibodies take some time to appear after infection, the tests may be repeated in 2 to 3 weeks to see if the antibody levels have become detectible (when initially absent) and to determine whether the levels are rising or falling over time.
This test may be required of a health care worker or a person starting college and is still ordered on women in some states as part of the blood testing required to obtain a marriage license.
TEST RESULTS
The Rubella titer is most useful as a screening tool to determine who is susceptible to Rubella and who is not. This is most important among women of childbearing age. Rubella acquired during a pregnancy carries significant risks for the fetus. Women who are contemplating pregnancy whose rubella status is unknown may benefit from this test. Those found to have no immunity can be immunized prior to pregnancy. Those women found to have no immunity to rubella during their pregnancy can be counseled to avoid contact with anyone known to have rubella, and can be immunized following delivery to protect them during any future pregnancy.
In an adult or child, the absence of IgG rubella antibodies means that the person likely has not been exposed to the rubella virus or been vaccinated and is not protected against it. The presence of IgG antibodies but not IgM antibodies indicates a history of past exposure to the virus or vaccination and indicates that the person tested should be immune to the rubella virus. The presence of IgG antibodies, but not IgM antibodies, in a newborn means that the mother's IgG antibodies have passed to the baby in utero and these antibodies may protect the infant from rubella infection during the initial six months of life. The presence of IgM antibodies in a newborn indicates that the baby was infected during pregnancy (because the mother's IgM antibodies do not pass to the baby through the umbilical cord). The presence of IgM antibodies, with or without IgG antibodies, in a child or adult indicates a recent infection with the rubella virus.
AGE IgM IgG INTERPRETATION
Normal Results: If the patient has been successfully immunized against rubella or has had the disease, the HI antibody titer (concentration) will be greater than 1:10-1:20. The red blood cells will fail to clump when the rubella virus is added to the blood serum.
In the case of paired testing for pregnant women, a fourfold rise in antibody titer between the first and second blood samples indicates the suspicious rash was caused by rubella. The alternative test for IgM antibody confirms recent rubella infection if IgM is found in the patient's blood.
Abnormal Results: If the patient has little or no immunity to rubella, her HI antibody titer will be 1:8 or less. Women without immunity should receive immunization against rubella provided that they avoid pregnancy for a period of three months following immunization. Women with disease of the immune system or who are taking corticosteroid medications should receive immune serum globulin rather than rubella vaccine to prevent infection.
These are general values taken from a variety of sources. The actual normal values may vary from lab to lab and from one type of testing protocol to another.
TITER RESULT INTERPRETATION Less Than (<) 1:10 No Immunity to Rubella 1:10 And Above Immune To Rubella
Occasionally, a patient will have a false positive test for IgM rubella antibodies because the test components cross react with other proteins in their body. To confirm the IgM result, the health care provider may order an IgG test to establish a baseline level of antibody and may repeat the IgG test again in 2-3 weeks to look for a significant increase in the amount (titer) present, indicating a recent rubella infection.
FURTHER TESTING
It is possible to test for the genetic material (RNA) of the virus directly in a sample or culture a body fluid sample, such as a throat swab, for the rubella virus. The rubella virus takes at least a week or more to be detected in culture, and special molecular assays or specifically prepared antibodies must be used to determine if the virus is present. This may occasionally be done to help a practitioner diagnose rubella infection in a newborn. Because this procedure is complex and expensive, most diagnostic laboratories refer this testing to a reference lab such as the Centers for Disease Control and Prevention (CDC). The number of cases of rubella and congenital rubella is monitored by the CDC to track the effectiveness of the rubella vaccine and to detect any outbreaks of the disease.
RUBELLA VACCINATIONS
NEW YORK (Reuters Health) - Over time, vaccine-induced rubella antibody levels decline and seronegativity rates rise, leaving children vulnerable to infection, public health officials report.
"Because rubella is a highly epidemic disease, vigilance will be required to assure continued elimination," Dr. Charles W. LeBaron of the Centers for Disease Control and Prevention, Atlanta and colleagues caution in the September 15 issue of the Journal of Infectious Diseases.
All states in the US require a second measles-mumps-rubella vaccine dose (MMR2), some at kindergarten entry and others at middle-school entry. In Wisconsin, where proof of MMR2 is required at both time points, the researchers analyzed pre- and post-vaccination serum samples collected in 1994-1995 from 307 children given MMR2 at ages 4 to 6 years and a comparison group of 306 children who received the booster at ages 9 to 11. The endpoint was persistence of antibodies at age 17.
The authors point out that at MMR2 administration, it had been 4 years since the first dose of the vaccine for the younger children and 10 years for the older group.
Before MMR2, the kindergarten children "had higher overall antibody levels" and a significantly lower incidence of negative titers: 9.4 vs 24.5 percent in the middle-school group.
After MMR2, 62 percent of the younger group and 66 percent of the older group showed a fourfold increase in titer, with the incidence of seronegativity reduced to less than 1 percent.
By age 17, both groups had antibody levels higher than their pre-MMR2 titers. However, the investigators found, the proportions with negative titers in both groups had fallen back to pre-MMR2 levels: 9.7 percent in the kindergarten group and 20.6 percent in the middle-school group.
They note that at each serum specimen collection and age, the younger group had significantly higher antibody levels than the older group, despite a much longer interval since the second dose, the researchers note.
"The possibility of rubella susceptibility among those whose titers have waned cannot be ruled out," the authors warn.
They conclude, "Because rubella is a highly epidemic disease, vigilance will be required to assure continued elimination."
Reference: J Infect Dis 2009;200:888-899.
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