Rubella Serology: Testing & Interpretation

Instructor: Lori Haag

Lori has teaching experience in the health care setting. She has an associate's degree in Nursing and a bachelor's degree in Psychology.

In this lesson you will learn about Rubella, tests used in diagnoses, and how to interpret these tests. You will also learn about the vaccination used to prevent a rubella infection.

That's a Good Question!

Most expectant mothers will do almost anything to protect their unborn child from harm. To ensure the health of a developing baby, taking prenatal vitamins, avoiding alcohol, and limiting caffeine have become common practices for pregnant women. So why is it that some of these same mothers refuse to take the necessary steps to protect their unborn child from things such as cataracts, heart defects, intellectual problems, and liver or spleen problems?

In 1998, Dr. Andrew Wakefield published an article about his research which linked the MMR vaccine to autism. The MMR is a combination vaccine administered to protect against measles, mumps, and rubella. Speculation about Dr. Wakefield's theory spiraled out of control, leading to false information regarding the vaccine and eventually an anti-MMR campaign by many parents. With a decline in vaccinations, disease numbers increased, leaving others at risk for contracting the diseases. Developing fetuses exposed to rubella are at the greatest risk because serious birth defects may occur.

Elimination Through Vaccination

Due in large part to the vaccination program that began in 1969, rubella is no longer endemic in the United States. In 2004, rubella was officially declared to be eliminated from the United States. A disease is considered to be eliminated when active disease transmission has not occurred for a period of 12 months. Less than 10 cases of rubella are reported in the United States each year, and evidence strongly suggests transmission of these cases did not occur in the United States.

Rubella Infection

Rubella is caused by a virus and spread from one person to another through infected secretions of a cough or sneeze. It can also be passed from a pregnant mother to her unborn child. People with rubella can be contagious for up to one week before symptoms appear and up to 7 days after symptoms begin. Rubella generally starts with a red rash on the face which spreads to other parts of the body. A low-grade fever, headache, swollen lymph nodes, cough, and runny nose may precede the rash by 1-5 days.

Illness from rubella is generally mild in children and adults, and as many as 50% of infected people display no signs or symptoms of illness at all. Developing fetuses, however, are extremely vulnerable to rubella because the virus may cause severe birth defects. This is known as Congenital Rubella Syndrome or CRS. If a pregnant woman contracts the disease, she may suffer a miscarriage or her baby may die soon after birth. Serious birth defects occur more commonly when infection takes place within the first trimester of pregnancy.

Pregnant women can pass rubella to their unborn children.


Vaccination against the rubella virus is the best way to prevent the disease. The vaccination stimulates the immune system to make antibodies against the virus, providing protection against the disease. The MMR is a combination vaccine which provides protection against measles, mumps, and rubella. The first dose of the vaccine is recommended at around 12-15 months and the second dose should be given between 4 and 6 years of age.

The MMR has helped eradicate rubella in the U.S.
MMR Vaccine

Immune System Response

In the presence of a rubella infection, the immune system will respond by producing antibodies against the virus. Serological tests can detect IgM antibodies which are useful in the diagnosis of an active infection. The optimum time to perform serological testing for rubella is approximately five days after the onset of the fever and rash. This is because the immune system has had time to respond and produce antibodies to the disease. At day five, 90% of serological tests will be positive for antibodies to rubella. This is compared to 50% of tests drawn on the first day of fever and rash.

IgG antibodies are also produced in response to a rubella infection. They are useful in determining whether an infection is active or a past infection has occurred. Low avidity IgG antibodies are detectable in the blood during an active or recent rubella infection. Avidity refers to how strongly an antibody bonds to its antigen. The higher the avidiity, the stronger the bond. High avidity IgG antibodies are not produced by the immune system until approximately three months after the beginning of a rubella infection. Therefore the presence of high avidity IgG antibodies indicates that a past infection had occurred at some point.

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