The Diagnostic Test
As the doctors who run medical laboratories, pathologists rely on different types of tests to diagnose and help with the management of COVID-19 in patients. For people showing symptoms or who may be infected, we use a type of test called PCR (polymerase chain reaction).
PCR testing analyzes the genetic material in the patient’s specimen, which is typically a sample of mucus collected from the back of the nose or throat. This enables us to identify the specific type of virus in the sample. These types of tests detect viral material to show that patients have or have recently been infected with the virus.
The Antibody Test
Also called serology tests, pathologists rely on this type of test to look for antibodies in the patient’s blood sample. These tests are not used for real-time diagnosis because it may take up to two weeks after exposure to the virus before your body starts producing antibodies.
We will be increasingly able to detect whether a person has COVID-19 antibodies, which may indicate they have some level of immunity. As with all lab tests, no test is perfect. Because there are other types of coronaviruses other than SARS-CoV-2, the virus that causes COVID-19, sometimes these tests can’t tell which coronavirus you have antibodies for. This would cause a false positive test, meaning you don’t have antibodies, but the test says you do.
If the prevalence of COVID-19 in the area you live in is low, it follows that your results are more likely to be negative because of decreased exposure. So, if your test comes back positive, that may be a false positive antibody test, and you should question it.
The challenge with COVID-19 is that the virus that causes it is completely new—doctors and clinical teams around the world have never seen it infect humans before. Because it is completely new, tests that could identify its precise genetic structure had to be developed—they had never existed before.
Since it is a new virus, we do not know if having antibodies for it really makes you immune. We don’t know for sure at which point a person who was infected is no longer infected, and of course, we don’t have a vaccine. Pathologists and infectious disease specialists around the world are working quickly and carefully to grow our understanding so we can make good decisions based on reliable antibody testing.
That depends on the type of test. A false negative on the PCR testing could mean, simply, you are disease-free that day. Depending on how you were tested, other factors could contribute to a false negative, these include procedures such as specimen collection, transport to the laboratory, and processes in the laboratory—which all must be followed according to strict protocols. If you test negative for a COVID-19 diagnostic test but later develop symptoms, contact your primary care physician.
As mentioned in the answer to question #1, above, testing for COVID-19 antibodies is currently less definitive than it is for better known viruses, such as those that cause mononucleosis or chicken pox. It is reasonable to expect antibody testing for COVID-19 to improve in the coming months, lowering the risks of false negatives or even false positives.
Turnaround time for test results is a common worry, especially when we’re concerned about an acute illness.
In the case of COVID-19, not all laboratories at all hospitals have the specialized equipment to perform molecular-level pathology tests. Some larger hospitals have those on site, but others must send the samples to outside labs for processing. Timing of receiving results will differ depending upon how the sample travels. The good news is that doctors and public health professionals are working quickly and effectively to help ensure that patients have ready access to testing and timely results.
Since testing recommendations change rapidly, please consult the Centers for Disease Control (CDC) and the U.S. Food and Drug Administration (FDA) for the most updated guidelines.