SARS CoV 2 Antibody Testing

A SARS-CoV-2 semiquantitative IgG test result is interpretated as positive at an index value of ≥1.00. The analytical measurement interval (reporting range) is 0.50 to 150.0 for the Siemens Atellica assay and 0.5 to 100 for the Siemens Centaur assay.6,7 A positive result means that an individual has developed an immune (IgG) response to recent/prior SARS-CoV-2 infection that is above the cutoff of the assay (1.00).6,7,16,17 Positive results may also occur after a COVID-19 vaccination, but the clinical significance of this finding is not yet fully understood.1,11-13 There are currently no FDA emergency use-authorized tests for individuals who have received a COVID-19 vaccination, and the performance characteristics of the current antibody tests have not been established for these individuals. Since much is still not known about the body’s immune response to this virus, this test result cannot be used to indicate a level of immunity/protection or rule out the chance for reinfection.1,5,15

This test should not be used to diagnose current SARS-CoV-2 infection.1,5,15 If a current infection is suspected, direct molecular or antigen testing for SARS-CoV-2 is necessary.1,3,5-7,16,17         

Index values reported as ˂1.00 are interpretated as negative. A negative semiquantitative antibody result means that the patient serum specimen has no SARS-CoV-2 spike IgG antibodies, or that the relative level of antibodies in the patient specimen is below the index cutoff.6,7

Note 1: The index value should not be interpreted as a measurement of durable immunity or protection from SARS-CoV-2 infection or reinfection.1,3,6,7 Durability and duration of immunity to SARS-CoV-2 are still not clearly defined and continue to be an area of national and global scientific and public health research.1,3 Results obtained with this assay may not be used interchangeably with values obtained with different manufacturers' test methods.1

Note 2: Tests performed after November 8, 2021, utilize an updated version of the SARS-COV-2 AB (IGG) SPIKE, SEMI QN assay (anti-S1 RBD,IgG assay [sCOVG]). Test results generated after this date are not equivalent to those generated on or before this date. The index value of the new assay’s calibration to the WHO 20/136 Standard in binding antibody units (BAU/mL) may be found in this reference: Freeman J, Conklin J. Standardization of two SARS-CoV-2 serology assays to the WHO 20/136 human standard reference material. J Virol Methods. 2022;300:114430. doi:10.1016/j.jviromet.2021.114430