Performance of a qualitative rapid chromatographic immunoassay to diagnose COVID-19 in patients in a middle-income country

J Clin Virol. 2020 Oct;131:104592. doi: 10.1016/j.jcv.2020.104592. Epub 2020 Aug 14.


Objectives: We evaluated a rapid chromatographic immunoassay (IgG/IgM antibodies) and an ELISA assay to diagnose COVID-19 in patient sat two Brazilian hospitals.

Methods: A total of 122 subjects with COVID-19 were included: 106 SARS-COV-2 RT-PCR-positive patients and 16 RT-PCR-negative patients with symptoms and chest computed tomography (CT) consistent with COVID-19. Ninety-six historical blood donation samples were used as controls. Demographic and clinical characteristics were retrieved from electronic records. Sensitivity and specificity were calculated, as were their 95% binomial confidence intervals using the Clopper-Pearson method. All analyses were performed in R version 3.6.3.

Results: The sensitivity of the chromatographic immunoassay in all RT-PCR-positive patients, irrespective of the timing of symptom onset, was 85.8% (95% binomial CI 77.7% to 91.9%). This increased with time after symptom onset, and at >14 days was 94.9% (85.9% to 98.9%). The specificity was 100% (96.4% to 100%). 15/16 (94%) RT- PCR-negative cases tested positive. The most frequent comorbidities were hypertension and diabetes mellitus and the most frequent symptoms were fever, cough, and dyspnea. All RT-PCR-negative patients had pneumonia. The most frequent thoracic CT findings were ground glass changes (n = 11, 68%), which were bilateral in 9 (56%) patients, and diffuse reticulonodular infiltrates (n = 5, 31%).

Conclusions: The COVID-19 rapid chromatographic immunoassay evaluated in this study had a high sensitivity and specificity using plasma, particularly after 14 days from symptom onset. ELISA and qualitative rapid chromatographic immunoassays can be used for the diagnosis of RT-PCR-negative patients.

Keywords: ELISA; SARS-cov-2; qualitative rapid chromatographic immunoassays.

Publication types

  • Evaluation Study
  • Multicenter Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Viral / blood*
  • Betacoronavirus
  • Brazil
  • Chromatography*
  • Clinical Laboratory Techniques
  • Coronavirus Infections / diagnosis*
  • Coronavirus Infections / immunology
  • Female
  • Hospitalization / statistics & numerical data
  • Humans
  • Immunoassay*
  • Immunoglobulin G / blood
  • Male
  • Middle Aged
  • Pandemics
  • Pneumonia, Viral / diagnosis*
  • Pneumonia, Viral / immunology
  • Prospective Studies
  • Sensitivity and Specificity
  • Young Adult


  • Antibodies, Viral
  • Immunoglobulin G

Supplementary concepts

  • COVID-19
  • COVID-19 diagnostic testing
  • severe acute respiratory syndrome coronavirus 2