Sensitivity of 3 ICT Assays Higher During Intermediate, Late COVID-19 Stages

SARS-CoV-2, COVID-19, coronavirus
Researchers compared 3 immunochromatographic assays (Sienna™, Wondfo®, and Prometheus™) to detect antibodies against SARS-CoV-2 in serum samples, using RT-qPCR as a reference.

Comparison of 3 immunochromatographic (ICT) assays for rapid detection of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) highlighted the importance of performing the serologic tests when the time since symptom onset was >1 week, as the sensitivity of the 3 ICT assays was higher during the second and third week of coronavirus disease 2019 (COVID-19), according to study results published in the European Journal of Clinical Microbiology & Infectious Diseases.

Researchers aimed to evaluate the following 3 ICT assays for immunoglobulin (Ig)M and IgG detection of COVID-19 in serum samples:

  • Wondfo® SARS-CoV-2 Antibody Test (Lateral Flow Method) (Guangzhou Wondfo Biotech Co., Ltd., Guangzhou Province, China)
  • Sienna™ COVID-19 IgG/IgM Rapid Test Cassette (T & D Diagnostics Canada Pvt, Ltd, Dartmouth, Nova Scotia, Canada)
  • Prometheus™ 2019-nCoV IgG/IgM Test Cassette (Prometheus Bio Inc., Zhejiang Province, China).

Investigators considered real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) the reference for evaluation of the ICT strip assays. They collected a total of 145 serum samples between March 8 and April 2 at the Hospital Universitario La Paz in Madrid, Spain, from 2 groups of patients: 95 healthcare workers and 50 patients admitted to the emergency department (ED) with a positive RT-qPCR or high clinical suspicion for COVID-19. Researchers analyzed the overall performance as well as 3 different stages according to the time since symptom onset: early stage (first week), intermediate stage (second week), and late stage (third week).

Researchers tested all 145 samples with Sienna, 117 with Wondfo, and 89 with Prometheus. They obtained overall results of sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), respectively, as follows:

  • Sienna: 64.4%, 75%, 85.5%, and 47.8%
  • Wondfo: 45.2%, 81.8%, 80.5%, and 47.4%
  • Prometheus: 75.5%, 12.5%, 51.4%, and 29.4%

The accuracy of the test was 67.6% with Sienna, 59% with Wondfo, and 47.2% with Prometheus, with a prevalence of COVID-19 of 69.7%, 62.4%, and 55.1% respectively.

When researchers performed the test in patients with <1 week (Sienna, n=67; Wondfo, n=63; Prometheus, n=60), between 7 and 14 days (Sienna, n=57; Wondfo, n=36; Prometheus, n=18), and >14 days (Sienna, n=18; Wondfo, n=15; Prometheus, n=10) since symptom onset, they obtained sensitivity, specificity, PPV, and NPV, respectively, as follows:

  • Sienna
    • Week 1: 36.6%, 84.6%, 78.9%, and 45.8%
    • Week 2: 81.3%, 55.6%, 90.7%, and 35.7%
    • Week 3: 100%, 66.7%, 75%, and 100%
  • Wondfo
    • Week 1: 18.9%, 88.5%, 70%, and 43.4%
    • Week 2: 74.1%, 55.6%, 83.3%, and 41.7%
    • Week 3: 83.3%, 88.9%, 83.3%, and 88.9%
  • Prometheus
    • Week 1: 68.8%, 8%, 51.1%, and 15.4%
    • Week 2: 90.9%, 14.3%, 62.5%, and 50%
    • Week 3: 100%, 25%, 25%, and 100%

Even though Prometheus presented a high sensitivity, the specificity was notably lower than the other 2 tests. Sienna showed the greatest contrast between sensitivity and

specificity, achieving the best accuracy, followed by Wondfo. In addition, the sensitivity of the 3 ICT assays was higher in the intermediate and late stages of the disease, highlighting the importance of performing the serologic tests when the time since the symptom onset is >1 week.

Considering the high rate of false positives when using Prometheus, investigators studied an extra 20 serum samples of randomly selected patients from 2018 as negative controls. Results confirmed a high percentage of false positive with Prometheus (35%); results for Sienna showed a much lower rate of false positives at 5%. Because of a lack of reagents, researchers did not perform this evaluation with Wondfo.

In addition to the interrupted availability of reagents, researchers listed 2 other key limitations. Differences between the group of healthcare workers and patients admitted to the ED may be a potential bias. In most healthcare workers, clinicians collected nasopharyngeal swabs and serum samples at the same time, and the time between symptom onset and serum sample collection was lower. On the other hand, patients admitted to the ED had a previous positive RT-qPCR or high clinical suspicion for COVID-19 and thus had more advanced stages of the disease, with higher rates of antibody production.

In addition, “the use of RT-qPCR as reference technique for the evaluation of serological test should be taken with care, since both techniques have different time windows for positivity during the course of the infection and RT-qPCR presented a substantial rate of false negatives,” noted the researchers.


Guedez-López GV, Alguacil-Guillén M, González-Donapetry P, et al; SARS-CoV-2 Working Group. Evaluation of three immunochromatographic tests for rapid detection of antibodies against SARS-CoV-2 [published online August 17, 2020]. J Clin Microbiol Infect Dis. doi:10.1007/s10096-020-04010-7

This article originally appeared on Infectious Disease Advisor