Just to put this in some context, but the Quest Diagnostics and other tests currently available are good but not great. For example, from their website there are the following disclaimers:
This test has not been reviewed by the FDA.
Positive results may be due to past or present infection with non-SARS-CoV-2 coronavirus strains, such as coronavirus HKU1, NL63, OC43, or 229E.
Negative results do not rule out SARS-CoV-2 infection, particularly in those who have been in contact with the virus. Follow-up testing with a molecular diagnostic should be considered to rule out infection in these individuals.
Results from antibody testing should not be used as the sole basis to diagnose or exclude SARS-CoV-2 infection or to inform infection status.
https://www.questdiagnostics.com/home/Covid-19/HCP/
Other sources state the following, however its important that not a lot of research has been done to validate the manufacturers specifications, of these tests such as specificity. Only over time and independent review will these numbers be more accurately quantified:
"The company started out using the Euroimmun AG Anti-SARS-CoV-2 ELISA IgG antibody test and then added the Abbott IgG antibody test. It is continuing to use both tests, although the Abbott test has become the primary platform. Euroimmun is a division of Perkin Elmer.
Both tests have received emergency use authorization from the FDA; only 10 serology tests have received this designation from the agency. The Euroimmun IgG test has a reported specificity of 96% and sensitivity of 65%, while the Abbott test claims a sensitivity of 100% and specificity of 99.5%. The FDA has just cracked down on serology tests requiring supporting validation documentation to be submitted within 10 business days of an initial notification."