I. How accurate is COVID-19 testing?

Testing for current and past COVID-19 infections is essential for ensuring that infected individuals get proper care; understanding and containing the disease’s spread, and developing treatments for this deadly new virus. However, testing only provides maximum benefits if it is accurate. At this stage of the pandemic, researchers and public health experts are questioning the accuracy of the existing COVID-19 testing methods.

How do they test for COVID-19?

Currently, there are two types of tests being deployed in the fight against COVID-19 — viral tests and antibody tests.

Viral tests diagnose active COVID-19 infections by identifying the disease’s genetic material. Most viral tests are nucleic acid tests, which look for the disease’s DNA in a mucus sample collected via nasal swab in a process known as reverse-transcriptase polymerase chain reaction (RT-PCR). The other type of diagnostic tests, antigen tests, detect viral proteins in a sample of saliva or tissue from the nasal cavity.

Antibody tests , also known as serological tests, analyze a blood sample for the presence of COVID-19 antibodies, which indicate that a person was infected with COVID-19, but has recovered.

While all of these tests have been useful in identifying current and past COVID-19 infections, they have also been vexed by inaccuracies in the form of false-negatives (returning a negative result when a person is, in fact, infected with COVID-19) and false-positives (when a test indicates that a person has or had COVID-19, but in reality, they do not).

Researchers have only begun to study the accuracy of COVID-19 tests, although there is abundant anecdotal evidence indicating that diagnostic tests are not always accurate. A study from Johns Hopkins Medicine, published in May, found that diagnostic tests can return false negatives anywhere from 20%-67% of the time, depending on what point in the infection a person is tested.

Inaccuracies in diagnostic tests are not uncommon, regardless of the diseases or conditions they are trying to detect. For example, according to Modern Healthcare, “rapid flu tests are known to miss 20% or more of all cases, a factor doctors weigh when treating patients who have symptoms but test negative.” However, as COVID-19 cases rise throughout the U.S., it is critical that test results be as accurate as possible to help slow the disease’s spread, and get infected individuals the treatment they need.

II. Why are COVID-19 tests inaccurate?

There are a few factors that affect the accuracy of COVID-19 diagnostic and antibody tests.

  • Rapid development of tests: Typically, the Food and Drug Administration (FDA) requires a significant review process to determine the tests’ accuracy before approving them for use. Because of the pandemic’s urgency, the FDA issued Emergency Use Authorization (EUA) to a number of diagnostic and antibody tests developed with limited understanding of the disease they were built to detect, and with only limited proof of their effectiveness and accuracy.
  • Timing: As the Johns Hopkins Medicine study indicates, when a COVID-19 test is conducted can impact the accuracy of the test results. If a diagnostic test is done before or after a person has detectable levels of the virus in their system, the test will likely return a negative result. Likewise, if a person has a serology test before their immune system produces antibodies, or after antibodies have fallen below detectable levels, there is a greater chance that their results will also be negative, even if they had COVID-19. Because of how new COVID-19 is, questions remain regarding how much time, post-infection, it takes to accumulate a detectable virus load, and how long antibodies stay present in an individual’s immune system, making it challenging for healthcare providers to identify the optimal timeframe for testing.
  • Sensitivity: This refers to how precise a test is in detecting the presence of COVID-19 RNA or antibodies in a sample. The more sensitive a test is, the more likely it will correctly identify the disease, even if the sample contains a limited amount of the virus or its antibodies. Less sensitive tests are more likely to return false-negatives, because they will not detect small amounts of infection or antibodies. Currently, the only FDA-approved antigen test has an 80% sensitivity rating, compared to 98% sensitivity of RT-PCR tests.
  • Specificity: This is a measurement of how well a test distinguishes between COVID-19 and other types of infection or antibodies. In the case of serology tests, they may incorrectly identify antibodies for other types of coronaviruses as COVID-19 antibodies, leading to a false-positive.
  • Specimen integrity: How a sample of a person’s mucus, saliva, or blood is collected, stored, and shipped can also affect the accuracy of test results. Collecting mucus and nasal fluid via nasal swab for a diagnostic test can be difficult, and samples must be shipped to labs quickly and at the correct temperature to prevent contamination and other issues that can affect the accuracy of test results.

III. What are the consequences of inaccurate COVID-19 testing?

The biggest concern with inaccurate COVID-19 diagnostic testing results is false-negatives in individuals who actually are infected with the disease. This could lead people, especially those who are asymptomatic, to behave as if they don’t have COVID-19, and not take the proper precautions to prevent further spread of the disease, including self-isolating and wearing masks.

Conversely, individuals who receive false-positive antibody test results may behave as if they have already had COVID-19, putting themselves at unnecessary risk of exposure.

Inaccurate test results also make it more difficult for epidemiologists and public health experts to get a complete picture of the disease’s spread, and effectively treat patients to contain outbreaks.

IV. Should you get tested for COVID-19?

Despite the fact that COVID-19 testing may be inaccurate, if you are experiencing symptoms of the disease, it is wise to seek testing, so that you can receive the proper treatment, and take the correct steps to avoid further spread of the disease.

The CDC and other public health experts are encouraging individuals who have symptoms to behave as if they are infected with COVID-19, regardless of whether they test positive or negative for the disease.

V. Additional Resources

Name Website Summary
Centers for Disease Control and Prevention (CDC) https://www.cdc.gov/coronavirus/2019-ncov/index.html The CDC is the United States’ leading national public health organization. Its mission is to protect public health and safety through the control and prevention of disease, injury, and disability in the U.S. and abroad.
World Health Organization (WHO) https://www.who.int/ A specialized agency of the United Nations, WHO is responsible for international public health. Headquartered in Geneva, Switzerland, it has field offices worldwide.
Association of Public Health Laboratories (APHL) www.aphl.org The APHL is a nonprofit organization in the United States that represents laboratories that protect public health and safety.

VI. Sources