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#267 Serology, Serology: How Accurate and Prevalent Art Thou?

What is the role of serology testing in the COVID-19 pandemic?

IgM and IgG antibodies may reveal an individual's recent (after ~2 weeks) exposure to COVID-19. How long serology remains positive and whether antibodies confer immunity to subsequent infection is unknown. Many different tests exist, each with different accuracy. Current evidence does not support routine use of serology testing in COVID-19 management.   

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Time to antibody seroconversion (after symptom onset): 
  • 85 hospitalized COVID-19 patients had 216 serial tests.1 
    • Sharp increase in positivity for IgM and IgG at ~2 weeks. 
    • IgM 90% positive at day 19, IgG >90% at ~1 month.  
  • 173 hospitalized COVID-19 patients had 535 serial tests.2 
    • Median time to seroconversion: IgM=12 days, IgG=14 days. 
    • Less than 7 days of illness: IgM ~40%. 
  • Limitations: short studiesunknown length of time IgG remains positive.  
Determining population prevalence of infection (including asymptomatic cases): 
  • Sampling of 865 people from Los Angeles35 antibody tests positive (~4%).3 
    • 4.7% after adjusting for sex, ethnicity, and income.
    • Black patients, those from households with low incomes, and symptomatic patients more likely to test positive.  
    • If results extrapolated to Canada,4 Canada would have 1.5-1.8 million cases. 
      • Currently have ~100,000.5 
  • Population based sampling in Geneva found ~10% of citizens antibody positive.6 
    • Estimate 11.6 seroconverted citizens for every confirmed COVID-19 case.  
Serologic test accuracy compared to PCR testing +/- CT  findings: 
  • Published: 
    • Sensitivity (truly have COVID-19 and antibody test positive):7,8 36%-99%. 
      • Depends on the test characteristics and when patient tested. 
    • Specificity (truly don’t have COVID-19 and antibody test negative):3,7 89%-99.5%. 
  • Health Canada Approved Tests:9 
    • Sensitivity after ~14 days of symptoms: 97.4%-100%. 
    • Specificity range: 98.5%-100%. 
  • Limitations: Results mostly from test companies’ in-house calculations.  
Does testing positive for COVID-19 antibodies confirm immunity? 
  • No studies have determined whether those who have had COVID-19 (as determined by IgG antibodies) have immunity to another COVID-19 infection. 
    • This will likely be answered in vaccine trials.
  • In the US, companies can bypass approval process to market their tests. 
    • Over 100 companies have marketed tests.10 
  • The sensitivity of serological testing in elderly or immunocompromised is unknown.11 
  • Serology should not routinely be used to diagnose acute COVID-19 infection.12 

Gilbert Bretecher June 5, 2023

no benefit to test for Covid 19

Gilbert Bretecher June 5, 2023

no benefit to testing for Covid 19 to confirm infection.

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  • Michael R Kolber MD CCFP MSc
  • Paul Fritsch MD CCFP

1. Xiang F, Wang X, He X, et al. Antibody detection and dynamic characteristics in patients with COVID- 19. Clin Infect Dis. 2020 Apr 19; ciaa461. doi: 10.1093/cid/ciaa461. [Epub ahead of print].

2. Zhao J, Zhao, Yuan Q, Wang H, et al. Antibody responses to SARS-CoV-2 in patients of novel coronavirus disease 2019. Clin Infect Dis. 2020 May 1; ciaa523. doi: 10.1093/cid/ciaa523. [Epub ahead of print].

3. Sood N, Simon P, Ebner P, et al. Seroprevalence of SARS-CoV-2-specific antibodies among adults in Los Angeles County, California, on April 10-11, 2020. JAMA. 2020 May 18; 323(23):2425-27. doi:10.1001/jama.2020.8279. [Epub ahead of print].

4. Stats Canada. Canadian population. Available at: Accessed June 10, 2020.

5. Johns Hopkins Coronavirus Resource Center. Available at: Accessed June 10, 2020.

6. Stringhini S, Wisniak A, Piumatti G, et al. Seroprevalence of anti-SARS-CoV-2 IgG antibodies in Geneva, Switzerland (SEROCoV-POP): a population-based study. Lancet. 2020 Jun 11. doi: 10.1016/S0140-6736(20)31304-0 [Epub ahead of print].

7. Dohla M, Boesecke C, Schulte B, et al. Rapid point-of-care testing for SARS-CoV-2 in a community screening setting shows low sensitivity. Public Health. 2020; 182:170-172.

8. Mahase E. Covid-19: Antibody test that claims to be 99% accurate is certified by EU. BMJ. 2020 Apr 29; 369:m1742. doi: 10.1136/bmj.m1742.

9. Farnsworth CW, Anderson NW. SARS-CoV-2 serology: much hype, little data. Clin Chem. 2020 Apr 28; hvaa107. doi:10.1093/clinchem/hvaa107. [Epub ahead of print].

10. Health Canada. List of authorized testing devices. Available at: Accessed June 10, 2020.

11. Statistics Canada. Testing devices for COVID-19: Serological testing devices. Available at: Accessed June 10, 2020.

12. Centers for Disease Control and Prevention. Coronavirus Disease 2019 (COVID-19). Interim Guidelines for COVID-19 Antibody Testing. Available at: Accessed June 10, 2020. 

Authors do not have any conflicts of interest to declare.

Les auteurs n’ont aucun conflit d’intérêts à déclarer.