Possible correlation of electrochemiluminescence based numerical cut off index value with concentration of anti-SARS-CoV-2 antibody: Is it worth reporting?

  • Shabnum Khawaja
    Department of Chemical Pathology, National Institute of Blood disease and Bone Marrow Transplantation (NIBD), Karachi, Pakistan.
  • Mohammad Asif
    Department of Haematology, National Institute of Blood disease and Bone Marrow Transplantation (NIBD), Karachi, Pakistan.
  • Samina Naz Mukry
    Department of Haematology, National Institute of Blood disease and Bone Marrow Transplantation (NIBD), Karachi, Pakistan.
  • Tahir Sultan Shaamsi
    Department of Haematology, National Institute of Blood disease and Bone Marrow Transplantation (NIBD), Karachi, Pakistan.


Background: Many laboratories are reporting a numerical cutoff index value (COI) value for most anti-SARS-CoV-2 qualitative tests. These numerical values in patients’ report ultimately created great confusion in the public and physicians, therefore this study was designed to evaluate the correlation of electrochemiluminescence (ECLIA) based numerical COI values with quantitative ELISA of anti-SARS-CoV-2 antibody.
Design and Methods: Two hundred and twenty-eight (228) recovered COVID-19 patients were included; their serum samples were analyzed by quantitative ELISA and ECLIA for anti-SARS-COV-2 antibodies.
Results: One hundred and seventy-three (75.8%) patients tested positive by ECLIA and ELISA assay and thirty-seven (6.2%) were tested negative by both methods. A weak positive correlation (r=0.37) was found between numerical COI value of ECLIA with ELISA concentration, which was statistically significant with p<0.001. All values were dispersed on scatter plot and there was no significant linear relationship between ECLIA and ELISA assay.
Conclusions: As both testing techniques are base upon the same immunological phenomena of detecting antibodies against nucleocapsid protein. We suggest that COI values are not meant to describe the immunity level of the individuals thus the physicians should not consider it as a quantitative value for antibody levels in COVID-19 patients.


WHO. General's opening remarks at the media briefing on COVID-19 – 11 March 2020. World Health Organization, 2020. Accessed: 11 Sep 2020. Available from: https://www.who.int/dg/speeches/detail/who-director-general-s-opening-remarks-at-the-media-briefing-on-covid-19—11-march-2020

Long QX, Tang XJ, Shi QL, et al. Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections. Nat Med 2020;26:1200-4. DOI: https://doi.org/10.1038/s41591-020-0965-6

European Centre for Disease Prevention and Control. Immune responses and immunity to SARS-CoV-2. 2020. Accessed: 28 Sep 2020. Available from: https://www.ecdc.europa.eu/en/covid-19/latest-evidence/immune-responses

Hick JL, Hanfling D, Wynia MK, et al. Duty to plan: health care, crisis standards of care, and novel coronavirus SARS-CoV-2. National Academy of Sciences, 2020. Available from: https://nam.edu/duty-to-plan-health-care-crisis-standards-of-care-and-novel-coronavirus-sars-cov-2/ DOI: https://doi.org/10.31478/202003b

AESKU.Group [Internet]. 6122 SARS-CoV-2 NP IgG. Accessed: 28 Sep 2020. Available from: https://www.aesku.com/index.php/diagnostics/aeskulisa-elisa-test-kits/infectious-serology-elisa/item/398

Silveira MF, Barros AJ, Horta BL, et al. Population-based surveys of antibodies against SARS-CoV-2 in Southern Brazil. Nat Med 2020;26:1196-9. DOI: https://doi.org/10.1038/s41591-020-0992-3

Nisar MI, Ansari N, Amin M, et al. Serial population based serosurvey of antibodies to SARS-CoV-2 in a low and high transmission area of Karachi, Pakistan. medRxiv 2020.

Roche Diagnostics [Internet]. Elecsys®Anti-SARS-CoV-2. 2020. Accessed: 28 Sep 2020. Available from: https://diagnostics.roche.com/global/en/products/params/elecsys-anti-sars-cov-2.html

Stites EC, Wilen CB. The interpretation of SARS-CoV-2 diagnostic tests. Med (N Y) 2020;1:78-89.

Hou H, Wang T, Zhang B, et al. Detection of IgM and IgG antibodies in patients with coronavirus disease 2019. Clin Transl Immunology 2020;9:e01136. DOI: https://doi.org/10.1002/cti2.1136

Liu X, Wang J, Xu X, et al. Patterns of IgG and IgM antibody response in COVID-19 patients. Emerg Microbes Infect 2020;9:1269-74. DOI: https://doi.org/10.1080/22221751.2020.1773324

Lippi G, Salvagno GL, Pegoraro M, et al. Preliminary evaluation of Roche Cobas Elecsys Anti-SARS-CoV-2 chemiluminescence immunoassay. Clin Chem Lab Med 2020;58:e251-3. DOI: https://doi.org/10.1515/cclm-2020-1042