Coronavirus Disease (COVID-19)
Serologic Testing

Serologic Testing

Notes

  • Nucleic acid amplification testing (NAAT) such as PCR remains the primary and most accurate way to diagnose acute COVID-19.
  • The utility of COVID-19 serology testing in clinical settings is unclear. It is not yet known whether the presence of IgG accurately predicts immunity to future infections.
  • While the sensitivity and specificity of the tests are presumed to be greater than >90% depending on the assay, the positive predictive value depends on the prevalence of the disease in a given population.
  • We do not know the overall prevalence of disease in Los Angeles. However, among patients with a high suspicion of past infection (including prior symptoms compatible with the disease and significant high-risk exposures), the test may have some modest utility in predicting true prior infection.
  • Serologies should not be used to gauge immunity.
  • Routine precautions must continue to be used even with a positive serology, including the use of enhanced droplet PPE when caring for patients with confirmed COVID-19 in the healthcare setting.

When to Consider

COVID-19 serologic testing could be considered for the following situations:

  • In the setting of suspected prior infection that was not tested by PCR.
  • Close contacts of high-risk patients (immunocompromised, elderly) who may have been exposed to the virus in the past
  • Healthcare workers or first responders
  • Patients residing in congregate settings that may have been exposed to or infected with the virus in the past, but who are not actively infected.
  • In the setting of potential plasma donation with prior diagnosed or suspected COVID-19.
  • In the setting of COVID-19-like illness where PCR is negative but clinical suspicion of disease remains high.
  • In the setting of suspected multisystem inflammatory syndrome in children (MIS-C).

When NOT to Use

COVID-19 Serology should not be used in the following settings:

  • When trying to diagnose acute COVID-19 (use PCR instead)
  • Testing of low-risk community patients (members of the general public) with no suspicion of recent infection who may simply be curious or want to know if they were infected.