What does your COVID-19 test result mean?
PCR? Antigen? Antibody? When it comes to the novel coronavirus, it’s easy to be confused on what test you need and what the result you get means.
Three main tests are available for COVID-19:
• The PCR test is part of a category known as the Nucleic Acid Amplification Tests, and it serves as a gold standard for COVID-19 testing. It provides evidence that someone is actively positive, and we call this a confirmed case.
PCR samples are obtained by a nasopharyngeal swab, and the procedure is rather invasive and uncomfortable. One of the disadvantages is a longer turnaround time compared to the other tests — up to 48 hours if a lab is not overwhelmed with samples.
• An antigen test is significantly quicker to return results: only 15-30 minutes. These tests are designed to detect protein material found on the surfaces of the coronavirus, whereas the PCR test detects viral genetic material.
Antigen tests are extremely specific, which means a positive result is highly likely to be accurate; however, because of low sensitivity, there is a greater chance of false negatives. Therefore, you cannot rule out infection with a negative antigen test, and you might need a PCR test for confirmation.
• An antibody test may not be able to show if you have a current infection because it can take up to three weeks after infection for your immune system to produce antibodies.
A positive antibody test result likely means you’ve been infected at some point in the past. We don’t know yet if having coronavirus antibodies can protect you from being re-infected with the virus, or how long any protection might last.
If you have a positive antigen result or a specific antibody result, your case is identified as a probable positive if the following clinical criteria are met:
At least two of the following symptoms: fever of at least 100 degrees, chills, myalgia, headache, sore throat, or a loss of taste or smell; or
At least one of the following symptoms: cough, shortness of breath or difficulty breathing; or
Severe respiratory illness with at least one of the following: clinical or radiographic evidence of pneumonia, or acute respiratory distress syndrome (ARDS) and no alternative more likely diagnosis.
If you have a positive antigen result or a specific antibody test but none of those symptoms, your case is listed as probable if you have at least one of the following exposures in the 14 days before your positive result:
Close contact with a confirmed or probable case of COVID-19;
Close contact with a person with clinically compatible illness and linkage to a confirmed case of COVID-19;
Travel to or residence in an area with sustained, ongoing community transmission of COVID-19; or
Member of a risk cohort as defined by public health authorities during an outbreak (e.g. symptomatic residents of a nursing home where at least one laboratory confirmed COVID-19 case has been identified).
When a person tests positive for COVID-19, the Office of Public Health conducts a thorough investigation of their recent contacts.
Anyone testing positive must isolate themselves until they are recovered and at least 10 days have passed. To be removed from isolation and considered recovered, the patient must be fever-free without medication at least three days and must show significant improvement in respiratory symptoms.
The household and community contacts are then quarantined for 14 days — for household contacts beginning with the positive case’s last day of isolation, and for others beginning with the last day of contact.
Household members should wait at least five days from the date of their loved one’s symptom onset to get tested.
Although the avalanche of COVID-19 news and updates can feel overwhelming, everyone can keep themselves and their communities healthy by taking these steps:
Limit yourself to necessary travel only, and avoid groups of more than 10 people and stay six feet apart from others when you do go out;
Wear face coverings in public to avoid transmitting the virus; and
Frequently wash your hands, use hand sanitizer when soap and water are not available, and avoid touching your face.
Together, we can stop the spread of COVID-19!
Anil Mangla is a Comal County epidemiologist.