Learn more. To maximize protection from the Delta variant and prevent possibly spreading it to others, get vaccinated as soon as you can and wear a mask indoors in public if you are in an area of substantial or high transmission. Updated Sept. Minus Related Pages. Summary of Recent Changes Updates as of September 21, Removed recommendation that persons in low-risk situations, with a positive antibody test within 3 months prior to a SARS-CoV-2 exposure or, tested immediately after an exposure do not need to quarantine.

Guidance for interpretation of antibody test results added in the form of a table. View Previous Updates.

On This Page. Current Status of Antibody Testing in the United States Antigenic targets While S protein is essential for virus entry into cells and is present on the viral surface, N protein is the most abundantly expressed immunodominant protein. Types of a ntibody t esting Different types of assays can be used to determine different aspects of the adaptive immune response and functionality of antibodies.

Binding antibody detection: These tests use purified proteins of SARS-CoV-2, not viable virus, and can be performed in lower biosafety level laboratories e. However, while IgM is most useful for determining recent infection, it usually becomes undetectable weeks to months following infection; in contrast, IgG is usually detectable for longer periods. IgA is important for mucosal immunity and can be detected in mucous secretions like saliva in addition to blood; although, its significance in this disease is still to be determined.

Depending on their complexity, some binding antibody tests can be performed rapidly in less than 30 minutes in a field setting or in a few hours in a laboratory. Tests that detect binding antibodies fall into two broad categories. Point-of-care POC tests are diagnostic tests performed at or near the place where a specimen is collected and can provide results within minutes rather than hours. Laboratory tests use lateral flow, ELISA, or chemiluminescent immunoassay CIA methods for antibody detection in serum, plasma, whole blood, and dried blood spots, which, for some assays, might require trained laboratory scientists and specialized instruments.

While most tests detect antibodies against either S or N proteins, some tests can detect antibodies against both immunodominant proteins multiplex assays. Neutralizing antibody detection tests determine the functional ability of antibodies to prevent infection by SARS-CoV-2 in vitro.

These tests monitor inhibition of viral growth in cell culture when incubated with serum or plasma. These tests may take up to 5 days to complete. These reporter-based tests can be performed in BSL-2 laboratories depending on the virus strain used.

These are binding antibody tests designed to qualitatively detect potentially neutralizing antibodies, often those that prevent interaction of the RBD with the ACE-2 receptor. These tests can be conducted in BSL-2 laboratories because they do not require viable virus. Top of Page. EUA tests include both qualitative and semi-quantitative tests. Antibody tests with very high sensitivity and specificity are preferred since they are more likely to exhibit high positive and negative predictive values when administered at least 3 weeks following onset of illness.

Additional considerations when selecting an antibody test include: IgG levels appear to decrease more slowly over time than levels of other classes of antibody. Therefore, assays that measure total antibody or IgG could have higher sensitivity as the time between infection and antibody testing increases. Persistence of detectable antibodies could vary by the test used. FDA has issued an EUA for a competitive neutralization test cVNT , a qualitative binding assay that detects antibodies that block the interaction between the virus and the cellular virus receptor ACE Although the cVNT exhibits correlation to a plaque reduction neutralization test PRNT , the clinical or public health applicability has not been established.

The clinical and public health applicability of semi-quantitative tests has not been established. Indications for antibody testing and interpretation of results Antibody testing is not a replacement for virologic testing and should not be used to establish the presence or absence of acute SARS-CoV-2 infection.

During this interval, the sensitivity of detecting infection using nucleic acid detection or antigen detection testing is decreasing and the sensitivity of serologic testing is increasing.

Antibody testing may be useful to support the diagnosis of COVID illness or complications of COVID in the following situations: A positive antibody test at least 7 days following acute illness onset in persons who had a previous negative antibody test e. A positive antibody test can help support a diagnosis when patients present with complications of COVID, such as multisystem inflammatory syndrome or other post-acute sequelae of COVID Therefore, when antibody tests are used to support diagnosis of recent COVID, a single positive antibody test result could reflect previous SARS-CoV-2 infection or vaccination rather than the most recent illness.

A health professional will usually draw the blood from a vein. For an infant, the blood may be obtained by puncturing the heel with a small needle lancet. If the blood is being drawn from a vein, the skin surface is cleaned with antiseptic, and an elastic band tourniquet is placed around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein usually in the arm inside of the elbow or on the back of the hand and blood is withdrawn and collected in a vial or syringe.

After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting blood for this test will only take a few minutes. Either method heel or vein withdrawal of collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a day or so.

The blood sample will be processed by a machine. The results are commonly available within a few days. If results suggest any abnormality, the doctor will likely perform further tests. The immunoglobulin test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn, like:.

Having a blood test is relatively painless. Still, many children are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear. Allow your child to ask the technician any questions he or she might have.

Tell your child to try to relax during the procedure, as tense muscles can make it harder and more painful to draw blood. It also may help for your child to look away when the needle is being inserted into the skin.

If you have questions about the immunoglobulin test, speak with your doctor. You also can talk to the technician before the procedure. Note: All information on KidsHealth is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. All rights reserved. It is possible to have a very low level of the virus in the body with a negative test result. This is a blood test. Antibodies are proteins produced by the immune system in response to an infection and are specific to that particular infection.

They are found in the liquid part of blood specimens, which is called serum or plasma. IgG antibodies remain in the blood after an infection has passed. These antibodies indicate that you may have had COVID in the recent past and have developed antibodies that may protect you from future infection.