Coronavirus Antibody Blood Test, from our experts to you.Dr Sam Rodgers MBBS, MRCGP
Chief Medical Officermeet our doctors
What is the Coronavirus Antibody Blood Test?
Our Coronavirus Antibody Blood Test is a laboratory test that measures the level of antibodies in your blood. It is called the Roche Anti-SARS-CoV-2-S coronavirus antibody test. You can use this test to monitor your antibody levels to record your response to the virus or the vaccine. This test is only available as a home finger-prick kit because clinic and nurse services are not permitted to collect venous samples for coronavirus antibody tests unless they are covered by UKAS accreditation. As our laboratory is UKAS accredited, we can offer this test with a self-collection finger-prick kit. Your anonymised data may be used to help UK public health agencies (including Public Health England) and other organisations understand the spread of coronavirus within the UK population.
What could my results show?
Your result will lie between 0.4 units per millilitre (U/ml) and 2,500 U/ml. A result below 0.8 U/ml means that the lab did not find antibodies in your sample. A result above 0.8 U/ml means that antibodies were detected, so you likely have had coronavirus (or have been vaccinated). It is possible to get a result below 0.8 U/ml even if you have had a coronavirus infection. This could be because you only experienced mild (or non-existent) symptoms. It could also be because your body responded to the virus using different parts of your immune system. There is a higher chance of a negative result (below 0.8 U/ml) if you take this test too soon after becoming infected with coronavirus or being vaccinated. This is because your body may not have had time to produce antibodies. We recommend waiting at least three weeks after a known infection or vaccination before taking this test. A negative antibody result cannot exclude a current infection. If you have recently been exposed to a coronavirus (such as SARS-CoV or COVID-19), the level of antibodies in your blood may not have yet reached levels that are high enough for this test to detect.
If you would like to monitor your antibody level over time, we recommend taking a test every three-four months. Several studies have shown that coronavirus antibodies remain in the blood for at least six-eight months for most people. For some, particularly people with no symptoms, antibody levels may decline more quickly.
How accurate is this test?
We use a CE marked Roche coronavirus antibody test called the Elecsys Anti-SARS-CoV-2 S assay. The manufacturer (Roche) carried out a study to support the CE mark submission of this test. The study used blood samples from patients with a positive coronavirus infection. Roche did not use samples from people without symptoms, so the results may have differed if the study had included these people.
Test sensitivity is the ability of a test to correctly detect a positive result when testing samples from people known to have had a coronavirus infection. Sensitivity can increase from the point of diagnosis because antibody levels increase in response to an infection. This means that from 21 days after a positive diagnosis (the earliest point at which we recommend testing), the test returned a positive result in 98.3% of cases. After 28 days, sensitivity is 100%, based on Roche’s study.
Test specificity is the ability of a test to correctly produce a negative result when testing samples from people known not to have had a coronavirus infection. Roche used 5,991 negative samples (which were collected before October 2019). The test produced only one false-positive result – giving the test a specificity of 99.98%.
This test may not accurately detect antibodies in people who have compromised immune systems because their antibody response may be slower or weakened. This includes people with immunodeficiency diseases, infections such as HIV, or those who take medications that suppress the immune system. This may also affect the sensitivity and specificity of the test.
How to prepare for your test?
Prepare for your Coronavirus Antibody Blood Test by following these instructions. Take this test at least 14 days after you developed symptoms of coronavirus, or 21 days after you were at risk of coronavirus infection.