Question: Do you have any information on antibody tests? Who are they useful for? Are there any published ranges for the test? I haven’t been able to find any. Getting antibody tests is the latest trend for my vaccine hesitant family. They are posting their test results online proudly and wanting their vaccinated friends to get the tests to compare scores. I’ve read that these tests are useless and cause false confidence. I also haven’t been able to find any guidelines on antibody test result ranges. If you’ve seen anything, please share. 

Answer: Antibody tests look for antibodies in your blood that fight SARS-CoV-2.  Such antibodies may be present after infection and/or after vaccination.  At the individual-level, antibody tests have limited usefulness and (like you write) can cause false confidence.  Per CDC, antibody testing is *not* recommended to identify whether a person has immunity to COVID either from previous infection or from vaccination; and people who have detectable antibodies but are not yet vaccinated *should* get vaccinated.  Some antibody tests are categorical (yes/no) while others are semi-quantitative.  The semi-quantitative tests have different ranges, and the the commonly used Roche assay has an upper cut-off of 250 AU/mL (AU/mL= absorbance unit per milliliter), with sample values ≥0.8 AU/mL being classified as positive.  None of the currently authorized antibody tests have been authorized to test individuals that have received a vaccine, and false negative results among vaccinated people are possible, especially depending on the test used (see Q&A of 2/17/21).  If you’d like to read more, take a look at CDC’s Interim Guidelines for COVID-19 Antibody Testing and its page on Testing for Previous Infection.