Clinical Significance of an IgM and IgG Test for Diagnosis of Highly Suspected COVID-19

Abstract

Background: Nucleic acid detection and CT scanning have been reported in COVID-19 diagnosis. Here, we aimed to investigate the clinical significance of IgM and IgG testing for the diagnosis of highly suspected COVID-19. Methods: A total of 63 patients with suspected COVID-19 were observed, 57 of whom were enrolled (24 males and 33 females). The selection was based on the diagnosis and treatment protocol for COVID-19 (trial Sixth Edition) released by the National Health Commission of the People's Republic of China. Patients were divided into positive and negative groups according to the first nucleic acid results from pharyngeal swab tests. Routine blood tests were detected on the second day after each patient was hospitalized. The remaining serum samples were used for detection of novel coronavirus-specific IgM/IgG antibodies. Results: The rate of COVID-19 nucleic acid positivity was 42.10%. The positive detection rates with a combination of IgM and IgG testing for patients with COVID-19 negative and positive nucleic acid test results were 72.73 and 87.50%, respectively. Conclusions: We report a rapid, simple, and accurate detection method for patients with suspected COVID-19 and for on-site screening for close contacts within the population. IgM and IgG antibody detection can identify COVID-19 after a negative nucleic acid test. Diagnostic accuracy of COVID-19 might be improved by nucleic acid testing in patients with a history of epidemic disease or with clinical symptoms, as well as CT scans when necessary, and serum-specific IgM and IgG antibody testing after the window period.

Keywords: COVID-19; CT scan; IgG; IgM; nucleic acid test.

Figure 1

IgM and IgG detection among the 33 patients with negative COVID-19 nucleic acid results. (A) The IgM-value of 20 patients was more than 0.88 U/L. (B) The IgG-value of 15 patients was more than 1.02 U/L.

Figure 2

IgM and IgG detection among the 24 patients with positive COVID-19 nucleic acid results. (A) The IgM-value of 19 patients was more than 0.88 U/L. (B) The IgG-value of 16 patients was more than 1.02 U/L.

Figure 3

Comparison of exposure times for NAAT and serological tests. (A) The SARS-CoV-2 exposure time between the nucleic acid amplification test (NAAT) positive group and the NAAT negative group. (B) The SARS-CoV-2 exposure time between the serological test positive group and the serological test negative group.

Figure 4

Combination of IgM and IgG detection of COVID-19. (A) The positive diagnostic rate with a combination of IgM and IgG detection for 33 patients with negative COVID-19 nucleic acid test results was 72.73%. (B) The positive diagnostic rate with a combination of IgM and IgG detection for 24 patients with positive COVID-19 nucleic acid test results was 87.50%.

Figure 5

Patient case CT scan. (A) For patient 55, the nucleic acid detection result was negative, but the IgM and IgG results were positive. In the lower regions of both lungs, large fuzzy shadows, GGO, and a slightly fan-shaped distribution were observed. (B) In patient 19, the nucleic acid detection result was positive, but the IgM and IgG results were negative, and no clear lesions were found in the lungs.

Figure 6

Association of CT results with PCR results and with serological results. (A) The proportion of positive NAAT between the positive and negative CT imaging groups. (B) The serological results between the positive and negative CT imaging groups.