Disclaimer: The aim of these rapid reviews is to retrieve, appraise, summarize and update the available evidence on COVID-related health technology. The reviews have not been externally peer- reviewed; they should not replace individual clinical judgement and the sources cited should be checked. The views expressed represent the views of the authors and not necessarily those of their host institutions. The views are not a substitute for professional medical advice.

Copyright Claims: This review is an intellectual property of the authors and of the Institute of Clinical Epidemiology, National Institutes of Health-UP Manila and Asia-Pacific Center for Evidence Based Healthcare Inc.

BACKGROUND

The COVID-19 infections are characterized by highly nonspecific manifestations including respiratory symptoms, fever, cough, difficulty in breathing. These symptoms are also seen as clinical presentations of other virus-related diseases including influenza.1,2

This poses a challenge in identifying those patients with COVID-19 from individuals with other respiratory diseases. Therefore, there is a need for a diagnostic test that is rapid, accurate and cost efficient that may be used at point-of-care to screen and confirm suspected cases. Early case detection has been proven to have a dramatic effect in controlling infectious disease outbreaks.3

The current, WHO-recommended gold standard for the diagnosis of COVID-19 is the qualitative detection of SARS-CoV-2 virus nucleic acid via reverse transcription polymerase chain reaction (RT-PCR). RT-PCR is reported to have a sensitivity of 95% and a specificity of 100%; for every 100 COVID-19 positive patients, RT-PCR would have a falsely negative result in 5 patients.4 The test,

however, has limitations such as long turnaround times and complicated logistical operations that makes it infeasible as a rapid and simple field test option to screen and diagnose patients. Another proposed rapid, simple, and highly sensitive way to diagnose COVID-19 is through the qualitative detection of antibodies that are specific to SARS-CoV-2 instead of the direct detection and measurement of viral load through RT-PCR.

Several studies have investigated the use of antibodies in the diagnosis of COVID-19 using ELISA5,6,7 and lateral flow rapid test kits.8,9 These studies show different sensitivity and specificity results, and different recommended timing of testing. Disparities between ELISA and lateral flow rapid test results may be due to the longer incubation time for ELISA compared to swift resolution for lateral flow tests, the slow kinetic dissociation rate of ELISA compared to a faster kinetic association rate in lateral flow tests, and the ELISA “capture” antibody and “detector” antibody designations may be reversed in lateral flow tests.10 Thus, results from studies using ELISA and lateral flow tests should be analyzed separately.

Arapid point-of-care lateral flow immunoassay test product was developed intended for qualitative detection of IgM/IgG in human blood within 15 minutes. It has been designed to be a complementary aid in the diagnosis of patients suspected to have the COVID-19 infection. Limitations of the test include the following: 1) it does not directly confirm virus presence, instead, it provides serological evidence of recent infection, 2) it is not known if the test will cross-react with antibodies to other coronaviruses and flu viruses.8 Further, studies in patients with Severe Acute Respiratory Syndrome (SARS), a disease also caused by a coronavirus, show that IgM is detectable as early as 3 to 6 days from symptom onset, while IgG is detectable after 8 days, with peak titers at 15 to 20 days.9,11 This potentially limits the clinical and public health utility of antibody tests for the early diagnosis of coronavirus infections.

Clinical trials that investigate the accuracy and safety of IgM/IgG rapid test kits for diagnosis of COVID-19 patients are still limited.

This rapid review summarizes the available evidence on the accuracy and safety of lateral flow immunoassay (LFIA) IgM/IgG rapid test kits in diagnosing patients with COVID-19. Evidence on the accuracy and safety of the enzyme-linked immunosorbent assay (ELISA) test for COVID-19 are summarized in a separate rapid review.

METHODS

Articles were selected based on the following inclusion criteria:

• Population: Symptomatic and asymptomatic COVID-19 patients and suspected COVID-19 patients of any age, with any comorbidities, any severity

•Intervention: Antibody/Antigen test, IgM/IgG rapid test kit

•Comparator: Reverse Transcriptase Polymerase Chain Reaction (RT-PCR)

•Outcomes: Sensitivity, Specificity, Time to detection of antibodies

•Methods: randomized controlled trials (RCTs), non- randomized studies, cohort studies, case-control studies, cross-sectional studies

RESULTS

Characteristics of Included Studies

After comprehensive search and appraisal, two (2) completed studies (Appendix 1) and one (1) ongoing trial (Appendix 2) on the accuracy of IgM/IgG antibody test kits for diagnosing COVID-19 were identified.

Li et al., examined 525 blood samples of clinically positive (including PCR test) (n = 397) and clinically negative (n = 128) patients to determine the sensitivity and specificity of the IgM/IgG rapid test kit.8 On the other hand, Ying et al., investigated 179 patients who were PCR positive (n = 90) and PCR negative (n = 89) comparing the over-all sensitivity and specificity of the antibody test kit and when done between day 0-7, day 8-15, or day 16 and beyond.9 In both studies, a positive test result was defined as detection of either or both IgM and IgG antibodies to SARS- CoV-2. A negative test result was defined as non-detection of any or both IgM and IgG antibodies to SARS-CoV-2.8,9

The ongoing trial (NCT04316728) is designed to evaluate the clinical performance of IgM/IgG antibody test kits in the early diagnosis of COVID-19 in high risk populations. The study will serially test uninfected health- care workers and individuals with chronic conditions (n=200) and is expected to complete data collection by September 2020.

Critical Appraisal

Two studies provided direct evidence on the accuracy of lateral flow immunoassay (LFIA) IgM/IgG rapid test kits in diagnosing COVID-19 compared with PCR and clinical picture as the reference standard. Both studies did not adequately describe the methods used to validate the accuracy of the test kits. As such, it is difficult to ascertain whether or not safeguards to ensure a good estimate of the test kit’s diagnostic accuracy were in place; the absence of these safeguards would tend to result in an overestimate of the test kit’s diagnostic accuracy. As such, the results of these two studies need to be interpreted with caution.

Accuracy Outcomes

The overall accuracy of the rapid test from the two identified studies are summarized below.

In majority of cases, Li et al. was not able to determine the number of days from symptom onset to the time the

blood sample for the rapid test was collected. However, in a subset of patients from one institution (n=58), the blood samples were collected at day 8 to 33 after symptom onset.8 Ying et al. reported the time from onset of illness to blood sample collection in 115 patients. The accuracy of the rapid test kit, stratified according to number of days of onset, is summarized below. The sensitivity (18.8%) of the rapid test was extremely low among those who had their blood

samples collected within the first week of symptom onset.9

Safety Outcomes

No adverse events were reported among the studies reviewed.

Recommendations from Other Guidelines

•The Chinese Center for Disease Control and

Prevention’s Laboratory Testing for COVID-19 Guideline stated that serum antibody tests are utilized as supplementary tests for the following conditions: a) cases that are negative for 2019-nCoV nucleic acid tests and used in addition to nucleic acid tests in diagnosing suspected cases and; b) serological and past exposure surveys of concerned population groups.12

•The World Health Organization recognizes the role of serological assays in research and surveillance but does not recommend it for COVID-19 case detection.13

•The European Centre for Disease Prevention and

Control states that SARS-CoV-2 antibody detection tests have limited usefulness in the early diagnosis of COVID-19 because it may take 10 days or more after onset of symptoms for patients to become positive.14

•Public Health England, does not recommend the use of rapid test kits for the diagnosis of COVID-19 infection in community settings.15

•The Public Health Laboratory Network of Australia does not recommend point-of care serology as first line tests in diagnosing acute viral infection due to significant limitations. Validated tests have some utility in determining past infection or screening purposes if used properly by a trained healthcare professional.16

•The National Institute of Infectious Diseases in Japan evaluated anti-SARS-CoV-2 antibodies in blood using

an immunochromatography method. They examined 37 cases of COVID-19 confirmed cases. It was found that virus-specific antibodies in COVID-19 patient sera are difficult to detect up to six days after onset of symptoms.17

•The United States Centers for Disease Control and Prevention recommends the PCR method in diagnosing COVID-19.18

•The Health Technology Assessment Council of the Department of Health recommended use of IgG and IgM Rapid Diagnostic Test for validation in the local setting and testing should be in parallel with RT-PCR.19

APPLICATION TO PRACTICE

•In patients with severe acute respiratory infection (ARI), and therefore a high pre-test probability, the rapid antibody IgM/IgG test may be more useful. To illustrate, in a patient with a pre-test probability of 70%, a positive test result (LR +: 9.46) will increase the post-test probability of COVID-19 to 96%. A negative test result (LR -: 0.13) on the other hand, will decrease the post-test probability of COVID-19 to 23%. (Appendix 4, Table 1)

•Conversely, in a patient with mild ARI assuming a pre- test probability of 10%, a positive rapid antibody IgM/ IgG test result will lead to a post-test probability of 51% and a negative test result will significantly decrease the post-test probability of COVID-19 to 1.4%. (Appendix 4, Table 1)

•However, on a national policy level, it is important to consider the implications of inadvertently labelling patients as false positives or false negatives. If we use the rapid antibody IgM/IgG test and it truly has the diagnostic accuracy reported in the studies (i.e., 90% sensitivity and 90% specificity), those who will test positive have a 10% chance that they might actually have no COVID-19 infection but will be misdirected to a COVID-19 referral hospital (false positive). There, the patient who actually does not have COVID-19 will be exposed to other patients who do have the infection. Conversely, if the rapid antibody test is negative, there

is a 10% chance that these patients might actually have COVID-19 and will be misdirected to a non- COVID ward in the hospital (false negative). There, the COVID-19-infected patient may potentially spread the infection to non-infected individuals.

•It is also important to note that the diagnostic accuracy of the IgM/IgG rapid test kit is at its best after the first week of symptom onset. This limits the usefulness of the test for identifying infected individuals early, to facilitate timely infection control measures and prevent further transmission of the disease.

Rapid Antibody Testing as a Screening Tool

In a hypothetical scenario of 1000 patients with respiratory symptoms and tested for COVID-19 using the IgM/IgG rapid testing kit, we determine the potential outcomes given the following assumptions based on the study of Ying [Ying]:

a.Sensitivity of 41% when IgM/IgG rapid testing is done within 15 days from onset of symptoms;

b.Specificity of 73% when IgM/IgG rapid testing is done within 15 days from onset of symptoms;

If the probability of COVID-19 infection in someone with respiratory symptoms is 20% (based on a consensus of infectious disease experts), the outcomes will be as follows, Figure 1:

1.298 patients will test positive for COVID-19 using the IgM/IgG rapid test and will be admitted to a COVID-19 hospital; but 216 (73%) of these patients are actually false positives and should not be in a COVID hospital.

2.702 patients will test negative for COVID-19 using the IgM/IgG rapid test and will be quarantined

in community isolation facilities; but 118 (17%) of these patients are false negatives and should be the ones in a COVID-19 hospital.

CONCLUSION

Current evidence does NOT support the routine use of IgM/IgG rapid test kits for the definitive diagnosis of COVID-19.

The diagnostic accuracy of the IgM/IgG rapid test kit varies greatly depending on the timing of the test relative to the number of days from symptom onset. The test performed very poorly (Sn: 18.8%, Sp: 77.8%,) during the early phase of the disease (i.e. less than eight days from onset of symptoms). As such, IgM/IgG rapid test kits are of limited use in the early diagnosis of COVID-19 and is unlikely to be a useful tool to minimize further transmission of the infection.

None of the reviewed guidelines recommend the routine use of IgM/IgG rapid test kits for the diagnosis of COVID-19.

Declaration of Conflict of Interest

No conflict of interest.

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9.Ying L, Yue-ping L, Bo D, Feifei R, Yue W, Jinya D, Qianchuan H. Diagnostic Indexes of a Rapid IgG/IgM Combined Antibody Test for SARS-CoV-2. 2020. https://www.medrxiv.org/content/10.1101/ 2020.03.26.20044883v1 [cited 2 Apr 2020]. Preprint

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12.Emergency Response Technical Centre. Laboratory testing for COVID-19 [Internet]. Chinese Center for Disease Control and Prevention. 2020 [cited 2020 Apr 2]. Available from http://www. chinacdc.cn/en/COVID19/

13.World Health Organization. Laboratory testing strategy recommendations for COVID-19 [Internet]. Laboratory testing strategy recommendations for COVID-19. 2020 [cited 2020 Apr 2]. Available from https://apps.who.int/iris/bitstream/handle/ 10665/331509/WHO-COVID-19-lab_testing-2020.1-eng.pdf

14.European Centre for Disease Prevention and Control [Internet]. An overview of the rapid test situation for COVID-19 diagnosis in the EU/EEA. 2020 [cited 2020 Apr 3]. Available from https://www. ecdc.europa.eu/sites/default/files/documents/Overview-rapid-test- situation-for-COVID-19-diagnosis-EU-EEA.pdf

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	No. Title/Author	Study	Country	Population
		design
	1 Li et al. 2020	Cohort	China	N = 525
	Development and	study		397 clinically positive
	Clinical Application			blood samples
	of a Rapid IgM-IgG
	Combined Antibody			128 clinically negative
	Test for SARS-CoV-2			blood samples
	Infection Diagnosis

	Intervention	Comparison	Key findings
	Group(s)	Group(s)
	IgM/IgG	RT-PCR	Sensitivity: 88.66%
	Rapid Test Kits		Specificity: 90.63%
			Positive Predictive Value: 96.70%
			Negative Predictive Value: 72.05%
			Positive Likelihood Ratio: 9.46
			Negative Likelihood Ratio: 0.13

Table 2. Characteristics of ongoing clinical trials

			Start and
	Clinical Trial		estimated	Study
No.		Status	primary		Country	Population
	ID / Title		completion	design
			date
1	NCT04316728	Not yet	Start date:	Clinical	Italy	n=200
	Clinical	recruiting	March 2020	trial		Negative patients defined
	Performance of		Est. primary			as adult HCWs with no
	the VivaDiag™		completion			signs or symptom of
	COVID-19 lgM		date:			coronavirus infection
	/ IgG Rapid		September			and no known previous
	Test in Early		2020			history of contact with
	Detecting					patients positive for
	the Infection					COVID-19, working in a
	of COVID-19					primary care setting; adult
						patients with at least 2
						chronic medical conditions
						routinely attending a
						General Practitioner (GP)
						practice or an outpatients
						departments or a primary
						care facility

Intervention Comparison

Group(s) Group(s)

VivaDiag™ PCR COVID-19 lgM/IgG

Rapid Test

Outcomes

•Number of patients with constant negative results

•Number of patients with positive test with a positive PCR for COVID-19

•Overall Number of patients positive for COVID-19

•Overall Number of patients negative for COVID-19

•Number of patients with contrasting results

PPatients who conform to the diagnostic criteria of suspected case of COVID-19 according to guideline of diagnosis and treatment of COVID-19 including typical epidemiological history and clinical characteristics

Symptomatic and asymptomatic COVID-19 patients and suspected COVID-19 patients of any age, with any comorbidities, any severity

What were the likelihood ratios of the various test results?

Day 0-7	Day 8-15	Day 16 or more
Sensitivity: 18.8%	Sensitivity: 100%	Sensitivity: 100%
Specificity: 77.8%	Specificity: 50.0%	Specificity: 64.3%
Positive Predictive Value: 60.0%	Positive Predictive Value: 85.7%	Positive Predictive Value: 93.2%
Negative Predictive Value: 35.0%	Negative Predictive Value: 100%	Negative Predictive Value: 100%
Positive Likelihood Ratio: 0.84	Positive Likelihood Ratio: 2.0	Positive Likelihood Ratio: 2.80
(Weakly Positive)	(Weakly Positive)	(Weakly Positive)
Negative Likelihood Ratio: 1.04	Negative Likelihood Ratio: 0	Negative Likelihood Ratio: 0
(Weakly Negative)	(Strongly Negative)	(Strongly Negative)