Clinical application of SARS-CoV-2 antibody detection and monoclonal antibody therapies against COVID-19

Table 2 Clinical significance of combined detection of severe acute respiratory distress syndrome coronavirus-2-specific antibodies and RNA

No.	Antibody assay		Nucleic acid detection	Clinical significance
	IgM	IgG
1	+	+	+	During the active infection period, the body has a certain resistance to COVID-19 (persistent IgG has been produced)
2	+	-	+	The patient may be in the middle of the SARS-CoV-2 infection. The body's immune response produces IgM antibodies early in the disease course. IgG has not yet been produced, or the IgG level has not reached the limit of detection
3	-	+	+	The patient may be in the middle or late phase of the disease or may have a recurrent infection of SARS-CoV-2
4	-	-	+	This is the COVID-19 "window period", which usually lasts 2 wk
5	+	+	-	The patient is in the recovery phase of COVID-19. The virus has been cleared from the body, and IgM and IgG are positive. Alternatively, this may indicate that the nucleic acid test result was a false negative, and the patient is in the active phase of infection
6	+	-	-	IgM positivity indicates that the patient may be in the early stage of infection. Suspicious nucleic acid test results require repeated sampling and verification
7	±	-	-	This indicates that the patient is in the early stage of viral infection, and the viral load is very low. The patient is in the acute stage of COVID-19, and the body has not yet produced IgG. Alternatively, the result for IgM may have been an error caused by the presence of rheumatoid factor. One week later, the examination and diagnosis must be repeated based to evaluate for changes in IgM and IgG
8	-	+	-	The patient may have been infected with the virus in the past and has recovered; the virus has been cleared from the body. IgG can last for a long time, possibly even for life
9	-	-	-	The individual is healthy or in the incubation period of infection

IgM: Immunoglobulin M; IgG: Immunoglobulin G; COVID-19: Coronavirus infectious disease 2019; SARS-CoV-2: Severe acute respiratory distress syndrome coronavirus-2.