What are coronavirus disease 2019 (COVID-19) antibody detection tests?

Updated: Apr 02, 2021
  • Author: James J Dunn, PhD, D(ABMM), MT(ASCP); more...
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Tests used to detect anti–SARS-CoV-2 antibodies in blood and saliva specimens are employed to identify patients currently or previously infected with SARS-CoV-2. In general, detectable levels of antibodies can take several days to weeks to develop; therefore, antibody detection tests have limited utility in the diagnosis of acute infection, with testing by NAAT being preferred for this. [7]  However, the use of antibody tests is viable as an aid to the diagnosis of COVID-19, even if the tests should not represent the sole basis for the determination of acute SARS-CoV-2 infection. [58, 59]  

Crucial to the interpretation of an antibody detection test is knowledge of the nature, dynamics, and timing of the antibody response to SARS-CoV2 infection. Several studies have shown that in most patients, seroconversion occurs by 2 weeks after the onset of symptoms; almost all patients have detectable levels of anti–SARS-CoV2 antibodies by day 28 post symptom onset. [60, 61] Studies involving hospitalized patients with SARS-CoV-2 infection confirmed by NAAT showed the presence of all isotypes of anti-SARS-CoV-2–specific antibodies, including immunoglobulin M (IgM), IgA, and IgG. [62] Detectable titers of IgM and IgA appeared 7-14 days post symptom onset (and in rare cases, as early as day one after symptom onset). The timing of peak IgG levels varies. In some cases, IgG can be detected simultaneously with IgM, but in the majority of patients it is delayed by a few days and plateaus between 15 and 21 days. [60] In most individuals, the antibody titer correlates with disease severity; however, some patients appear to have undetectable levels of antibodies. [58, 63]

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