2 Types of Testing Procedures

Molecular (Diagnostic) Test
Detects the presence of an active pathogen (e.g. virus) or part of a virus. Used for diagnosing disease (e.g. SARS-CoV-2 PCR Test)

Serological (Antibody) Test
Detects whether one has been exposed to a pathogen and has cleared the infection

Molecular (Diagnostic) Test

Recent studies have shown that concentrations of virus (viral loads) vary in different areas of the body.

  • Lower Respiratory Tract Sample: 93% positive (likely due to SARS-CoV-2 preference of infecting the lower respiratory tract)

  • Sputum Sample: 72% positive

  • Nasal Swab Sample: 63% positive

  • Throat Swab Sample: 32% positive

Since studies have shown that negative nasopharyngeal and oropharyngeal swab samples alone do not rule out COVID-19, after a physician uses his/her judgement with regards to whom to test (taking into account the patient’s travel and / or exposure, local COVID-19 activity, and other various risk factors), the following procedures are initiated:

  • Specimens are obtained from the upper respiratory tract : nasopharyngeal swab (this is recommended) is placed into the nostril and left there for a few minutes for secretion to be absorbed. If using an oropharyngeal swab, the specimen is obtained from the back of the mouth, while avoiding the tongue and tonsils. 

  • Lower Respiratory Tract: Specimens are obtained using bronchoalveolar lavage or aspiration from the trachea. A deep productive cough (sputum sample) is also acceptable.

  • Blood Sample

All three of the above are submitted for the identification of SARS-CoV-2 RNA via the Polymerase Chain Reaction (PCR) test to confirm the diagnosis. All suspected cases of COVID-19 should be reported to appropriate public health authorities (local or state health department).

In those patients with laboratory proven COVID-19 disease, repeat testing is recommended to establish proper clearance of the virus, which by definition is two consecutive negative PCR test results at least 24 hours apart.

Saliva Test - FDA approved on 4/13/2020.

Serological (Antibody) Test

A blood test which will allow one to know if they have been exposed to SARS-CoV-2 in the past and have cleared the infection.

  • IgM antibodies are produced by the body 6-10 days post exposure to SARS-CoV-2 and peak at day 12, staying in the body for up to 35 days, after which their levels decline

  • IgG antibodies (memory) peak at day 17 post exposure to SARS-CoV-2 and last for greater than or equal to 49 days. For comparison, IgG antibodies have been found to be present in patients who have recovered from SARS infection two years later.

This will allow people, if asymptomatic, to return to the workplace without fear of infecting others. It is uncertain whether the presence of antibodies always correlates to future protection from disease.

It is possible that a person’s antibody response may not be strong enough to prevent future disease and even if initially strong enough, it is not known how long the immunity will last.

There are currently multiple antibody (serology) tests on the market, but none have been validated and proven accurate by the FDA (many are currently being evaluated). In an effort to increase the accuracy of antibody testing, as of May 5, 2020, the FDA has updated its policy, now requiring companies that are developing new tests to apply for Emergency Use Authorization (EUA) through the FDA.

Early models of antibody tests have been proven to be inconsistent in their accuracy and quality. Nearly all antibody tests attempt to detect the S protein of SARS-CoV-2, with a few also incorporating the N protein. Unfortunately, early in infection, the levels of the S protein are not uniform and are found in much lower levels in these patients. A recent study has shown that besides the S protein, there are other SARS-CoV-2 proteins that promote an antibody response in COVID-19 patients, specifically early in the disease (day 4 of infection). These proteins, specifically the N, ORF 3b, ORF8, when detected together, have a 100% sensitivity and specificity to SARS-CoV-2. The latter two proteins are unique to SARS-CoV and SARS-CoV-2 and not other coronaviruses, therefore reducing cross-reactivity issues that other antibody tests might face. This data suggests that future antibody testing could incorporate these other novel protein antigen targets of SARS-CoV-2 over and above the S protein, therefore allowing for more accurate results even early in the disease state when the S-protein has limited sensitivity.