EUA Authorized Serology Test Performance
About this page
Serology tests detect the presence of antibodies in the blood when the body is responding to a specific infection, like COVID-19. In other words, the tests detect the body?s immune response to the infection caused by the virus rather than detecting the virus itself. In the early days of an infection when the body?s immune response is still building, antibodies may not be detected. This limits the test?s effectiveness for diagnosing COVID-19, and this is one reason serology tests should not be used as the sole basis to diagnose COVID-19. Serology tests could play a role in the fight against COVID-19 by helping healthcare professionals identify individuals have developed an immune response to SARS-CoV-2. In addition, these test results can aid in determining who may donate a part of their blood called convalescent plasma, which may serve as a possible treatment for those who are seriously ill from COVID-19. However, to use these test properly, it is important to understand their performance characteristics and limitations. Moreover, studies are underway to address questions that will better inform the appropriate use of these tests, such as whether the presence of antibodies conveys a level of immunity that would prevent or minimize the severity of re-infection as well as the duration for which immunity lasts. The performance of these tests is described by their ?sensitivity,? or their ability to identify those with antibodies to SARS-CoV-2 (true positive rate), and their ?specificity,? or their ability to identify those without antibodies to SARS-CoV-2 (true negative rate). A test?s sensitivity can be estimated by determining whether or not it is able to detect antibodies in blood samples from patients who have been confirmed to have COVID-19 with a nucleic acid amplification test, or NAAT. In some validation studies of these tests, like the one FDA is conducting in partnership with NIH, CDC, and BARDA, the samples used, in addition to coming from patients confirmed to have COVID-19 by a NAAT, may also be confirmed to have antibodies present using other serology tests. A test?s specificity can be estimated by testing large numbers of samples collected and frozen before SARS-CoV-2 is known to have circulated to demonstrate that the test does not produce positive results in response to the presence of other causes of a respiratory infection, such as other coronaviruses. These estimates of sensitivity and specificity are just that: estimates. They include 95% confidence intervals, which are the range of estimates we are about 95% sure a test?s sensitivity and specificity will fall within given how many samples were used in the performance validation. The more samples used to validate a test, the smaller the confidence interval becomes, meaning that we can be more confident in the estimates of sensitivity and specificity provided. Tests are also described by their Positive and Negative Predictive values (PPV and NPV). These measures are calculated using a test?s sensitivity, its specificity, and using an assumption about the percentage of individuals in the population who have antibodies to SARS-CoV-2 (which is called ?prevalence? in these calculations). Every test returns some false positive and false negative results. The PPV and NPV help those who are interpreting these tests understand, given how prevalent individuals with antibodies are in a population, how likely it is that a person who receives a positive result from a test truly does have antibodies to SARS-CoV-2 and how likely it is that a person who receives a negative result from a test truly does not have antibodies to SARS-CoV-2. The PPV and NPV of a test depend heavily on the prevalence of what that test is intended to detect. Because all tests will return some false positive and some false negative results, including tests that detect antibodies to SARS-CoV-2, broad use of the tests, when not appropriately informed by other relevant information, such as clinical history or diagnostic test results, could identify too many false-positive individuals. We do not currently know the prevalence of SARS-CoV-2 antibody positive individuals in the U.S. population, and prevalence may change based on the duration the virus is in the country and the effectiveness of mitigations. Moreover, prevalence may vary widely between locations and between different groups of people, such as health care workers, due to different rates of infection. In low prevalence populations, which will be much of the asymptomatic general population, the result of a single antibody test is not likely to be sufficiently accurate to make an informed decision regarding whether or not an individual has had a prior infection or truly has antibodies to the virus. A second test, typically one assessing for the presence of antibodies to a different viral protein, generally would be needed to increase the accuracy of the overall testing results. For this page, FDA has summarized the expected performance of the tests it has authorized based on the information FDA reviewed when deciding whether or not to grant these tests an Emergency Use Authorization and assuming a prevalence of 5% for PPV and NPV calculations. For tests that had multiple validation studies or where the tests showed variable performance in samples collected at different times after symptom onset, FDA experts selected the results they considered to be most representative of expected test performance. This is an incomplete representation of the performance of these tests.?Always refer to the complete instructions for use to put these estimates into the proper context?and to understand how to use and interpret these tests. FDA also is providing a?calculator?that will allow users to see the estimated performance of a single test or two independent tests based on their performance characteristics and the estimated prevalence of SARS-CoV-2 antibodies in the target population.Test Performance
Abbott Architect SARS-CoV-2 IgG
Developer:?Abbott Test:?Architect SARS-CoV-2 IgG Technology:?High Throughput ELISA| Antibody | Performance Measure | Estimate of Performance | 95% Confidence Interval |
|---|---|---|---|
| IgG | Sensitivity | 100% (88/88) | (95.8%; 100%) |
| IgG | Specificity | 99.6% (1066/1070) | (99%; 99.9%) |
| IgG | PPV at prevalence = 5% | 92.9% | (83.4%; 98.1%) |
| IgG | NPV at prevalence = 5% | 100% | (99.8%; 100%) |
Autobio Anti-SARS-CoV-2 Rapid Test
Developer:?Autobio Test:?Anti-SARS-CoV-2 Rapid Test Technology:?Lateral Flow| Antibody | Performance Measure | Estimate of Performance | 95% Confidence Interval |
|---|---|---|---|
| IgM | Sensitivity | 85.4% (346/405) | (81.7%; 88.5%) |
| IgM | Specificity | 99.7% (311/312) | (98.2%; 99.9%) |
| IgG | Sensitivity | 86.2% (349/405) | (82.5%; 89.2%) |
| IgG | Specificity | 99.4% (310/312) | (97.7%; 99.8%) |
| Combined | Sensitivity | 88.1% (357/405) | (84.6%; 90.9%) |
| Combined | Specificity | 99% (309/312) | (97.2%; 99.7%) |
| Combined | PPV at prevalence = 5% | 82.9% | (61.4%; 94.1%) |
| Combined | NPV at prevalence = 5% | 99.4% | (99.2%; 99.5%) |
