COVID-19 IgG/IgM Rapid Test Kit
SARS-CoV-2, causing COVID-19, has emerged to cause a human pandemic. Detection of SARS-CoV-2 in respiratory samples by using PCR is the standard laboratory diagnostic tool. Our aim was to perform a limited evaluation of the diagnostic performance and user-friendliness of eleven rapid tests for detection of antibodies against SARS-CoV-2.
All participants were tested with PCR against SARS-CoV-2 at a clinical microbiology laboratory. Comparing with results from PCR tests, we evaluated the rapid tests’ performances in three arms; 1) 20 hospitalized patients with PCR-confirmed COVID-19, 2) 23 recovered outpatients with former PCR-confirmed COVID-19, and 3) 49 participants with suspected COVID-19 presenting at a primary care emergency room.
All eleven tests detected antibodies in hospitalized COVID-19 patients, though with varying sensitivities. In former outpatients recovered from COVID-19, there were differences between tests in the immunoglobulin type G (IgG) sensitivity, with five tests having a sensitivity below 65%. In participants with suspected COVID-19 infection, the rapid tests had very low sensitivities. Most rapid tests were easy to perform and interpret.
Rapid tests were not suited as stand-alone tests to detect present infection in a Norwegian primary care emergency room population. All the rapid tests were able to detect SARS-CoV-2 antibodies, although sensitivities varied and were generally higher in the study arm of more severely affected participants. Rapid tests with high IgG sensitivity (and specificity) may be useful for confirmation of past infection. An independent evaluation should be performed in the intended population before introducing a rapid test.
In December 2019, Wuhan city in Hubei Province, China, became the center of an outbreak of a severe pneumonia, later named Coronavirus Disease 2019 (COVID-19), and identified as caused by a novel coronavirus SARS-CoV-2. The coronavirus was isolated, and full-genome sequencing showed a betacoronavirus in the subgenus sarbecovirus . Human-to-human transmission of SARS-CoV-2 occurs primarily through respiratory droplets. Due to the rapid spread of the virus, the World Health Organization declared COVID-19 a worldwide pandemic by February 2020. The clinical presentation of COVID-19 varies from asymptomatic disease, via mild upper respiratory infection to severe pneumonia with respiratory failure and death.
Molecular diagnostic tests with real-time PCR are used to identify SARS-CoV-2 RNA in respiratory samples. PCR is performed at medical microbiology laboratories, requiring advanced analytical instruments and trained personnel. Shortage of sampling equipment and necessary reagents has periodically limited the number of people being tested for COVID-19 in Norway.
Detecting humoral immune response to the virus is a different analytical approach. Generally, immunoglobulin type M (IgM) is produced during the early stages of an infection, usually followed by production of immunoglobulin type G (IgG). For infection with SARS-CoV-2, however, there is some evidence that IgG may be detected at the same time as IgM, or even earlier , .
Several enzyme immune assays (EIA) or chemiluminescent immunoassays (CLIA) for detection of antibodies against SARS-CoV-2, both commercial and in-house, will are becoming available in Norwegian hospital laboratories. At the same time, a substantial number of point-of-care rapid tests (lateral flow immunoassays) are currently being marketed. Even though most of the rapid tests are CE/IVD approved, they generally come with very limited documentation on test performance, and only rarely with any manufacturer independent evaluation , , .
Our aim was to perform a limited evaluation of the diagnostic performance of a selection of rapid test for COVID-19 in different clinical settings, and in particular to evaluate if the tests could be used to confirm past infection. Further, we wanted to assess user-friendliness.
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Materials and methods
The evaluation was organized as a quality assurance study in a collaborative effort between the municipality of Kristiansand, the Norwegian Institute of Public Health, and the Norwegian Organization for Quality Improvement of Laboratory Examinations (Noklus). The eleven rapid tests chosen for evaluation were a convenience sample, consisting of the tests that could be delivered to Noklus before the set deadline of April 1st, 2020 (Table 1). Suppliers provided their tests free of charge to Noklus and did not pay for the evaluation. In sending the tests, they consented to having the results published.
This was a quality assurance study, and we used anonymized data. The project was approved by the data protection officer at each test site. Informed verbal consent was obtained from the patients in study arms two and three at collection of blood samples.
In the 20 hospitalized patients in study arm 1, the number of days since onset of symptoms was <7 for one patient, 7–13 days for three patients, and 14+ days for 16 patients. In study arms 2 and 3, the median number of days since onset of symptoms was 30 (range 27–36) and 8 (range 2–34), respectively. Of the 23 participants in study arm 3 with a positive PCR test, thirteen had <7 days since onset of symptoms, six had 7–13 days, and four had 14+ days.
Results from hospitalized patients (study arm 1) showed that all the eleven rapid tests detected SARS-CoV-2 IgM and/or IgG antibodies in this population, though with varying sensitivities (Tables 2 and 3). Study arm two consisted of participants who had recovered from PCR-confirmed COVID-19 without requiring hospitalization. In this population, tests A, B, C, and D had higher IgG positivity rates than tests E, F, H I, and J. Confidence intervals (80%) for test K were overlapping with the others (Table 3). Five of the tests had a sensitivity below 65% for IgG.