Updated on May 13th, 2021 with summary table on COVID-19 tests and their sources at the bottom.

Executive summary

  • A diagnostic test directly affirms the presence of the COVID-19 virus
  • Rapid (molecular), antigen and antibody tests were deployed for more widespread testing at a lower cost to develop baseline infection rates, especially in outbreak or congregate settings, such as nursing homes and schools. They maybe less accurate than the diagnostic test
  • If you have symptoms or COVID-19 exposure, it is recommended you get a diagnostic test

Quite quickly, the different types of COVID-19 tests caused me confusion as to which one I would need and when. In New York City, there is a one-size-fits-all message to get tested. It is recommended by the Test & Trace Corps (published January 6, 2021) to get tested immediately if you have symptoms or (possible) exposure, and periodically if you work outside of your home. However, it is still not clear which test you should get.

The antigen test is recommended (published October 17, 2020) in New York State for use in congregate settings like nursing homes and schools. It is relatively less expensive but less sensitive than a diagnostic test. However, there are recommendations to get the diagnostic test as a confirmation of a positive result. A rapid molecular test was also developed to be used in contexts like nursing homes and schools, similar to the antigen test, and it also recommends a confirmatory diagnostic test for positive results.

New York State uses the antibody test to develop a baseline infection rate. The test developed by the state detects antibodies in the blood, specifically IgG, which is usually developed three to four weeks after infection. It is not recommended to take this test until twenty-one days after a positive diagnostic test or the symptoms of COVID-19 started. Only the diagnostic test itself detects the virus’ genetic makeup.


Updated on May 13th, 2021 with summary table on COVID-19 tests and their sources.

 
Test
 
Nucleic acid amplification (e.g. RT-PCR)
 
Antigen
 
Antibody
TypeDiagnostic, detects virus’ DNADiagnostic, detects spike protein on virus’ surfaceNon-diagnostic, detects antibodies fighting against virus
UseMost accurate for current infectionLess accurate but more affordable for current infectionCheck for prior infection (requires 1-3 weeks after infection)
ScenarioKnown exposure or symptoms; lab version to confirm less accurate test (positive, or symptomatic but negative test from antigen or non-laboratory version)Known exposure or symptoms; high-risk congregate settings; routine screeningSurveillance
Vaccinated alreadyWill not test positiveMay be exempted from routine screeningMay test positive, so cannot assess immunity
Turnaround time1-2 days15 minutes30 minutes (field) to 2 hours (lab)
Cost (government benchmark cash prices)Non-High Throughput: $51.31
High Throughput: $100 ($75 if not done within 2 calendar days)
$45.23 (e.g. ELISA)Multi-step: $42.13
Single-step: $45.23

Sources:

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