Sensitivity of point-of-care IgM and IgG test in critically ill patients with SARS-Cov-2

Dear Editor, The severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) pandemic requires accurate diagnostic tests to triage patients between properly isolated and regular wards [1]. Gold-standard tests are based on reversetranscriptase polymerase chain reaction (RT-PCR) performed on nasopharyngeal swabs [2]. Quick serology tests detecting immunoglobulin M and G (respectively IgM and IgG) targeted against SARS-Cov-2 are also available [3, 4]; however, concerns have been raised on their sensitivity in intensive care units (ICU), where patients are more severe and some immunosuppressed. In this multicenter observational study, we assessed sensitivity of a point-of-care serology test (POCST) regarding SARS-Cov-2, in ICU patients presenting severe SARSCov-2 infection. All included patients were positive for SARS-Cov-2 using routine RT-PCR methodology. POCST was sampled with finger prick, with 10 μL of blood and tested with the device, BIOSYNEX COVID-19 BSS (IgG/ IgM)® (Biosynex, Illkirch-Graffenstaden, France). Each POCST incorporated a quality control. Concordance between RT-PCR and POCST was assessed regarding the presence of IgM and/or IgG. Patients for whom POCST showed no IgM and no IgG were considered negative. The study was approved by institutional review board (00012608-2020-01) and registered under clinicaltrials.gov identifier NCT04467008. Overall, 99 patients were included. Patients were 62.4 ± 13.3 years old, 34.7% were women, and average body-mass index (BMI) was 29.1 ± 5.9 kg/m. Mean Simplified Acute Physiological Score II (SAPS II) was 50.1 ± 22.8. Average delay between POCST and first symptoms was 17.9 ± 9.1 days (see baseline characteristics in Table 1). Results were obtained in less than 10 min for all, except in 2 (2.0%) in whom quality control was not met; hence, tests required to be performed twice. The POCST yielded 8 (8.1%) negatives, corresponding to a sensitivity of 91.9%. Delay between first symptoms and POCST was significantly lower in negative than positive patients (10.4 ± 7.8 vs 18.6 ± 7.9 days, p = 0.005) (see Fig. 1 a). Negatives were significantly younger (50.7 ± 16.9 vs. 63.5 ± 12.5 years old, p = 0.009). Rest of variables were similar, including lymphocytes’ count (1.0 ± 0.7 vs 2.4 ± 8.5 G/L, p = 0.55) (see Table 1 and Fig. 1). Multivariable logistic regression showed that both delay and age were independently associated with negative POCST (respectively adjusted odds-ratio, 0.82 (0.71–0.95) per 1-day increase, p value = 0.009, and 0.93 (0.87–0.98) per 1-year increase, p value = 0.013). The other three different serology profiles were IgM+/ IgG− in 7, IgM+/IgG+ in 64, and IgM−/IgG+ in 19 patients. Delay between first symptoms and POCST was significantly different across all four groups. Contrary to SAPS II, distribution of age, BMI, and lymphocytes’ count did not significantly differ across all four groups (see Fig. 1b–d). In this observational study in ICU patients, sensitivity of POCST was similar to specifications provided by the manufacturer (93%). Variables associated with negative results were age and delay between onset and POCST which was expected given known dynamics of immunization after SARS-Cov-2 infection [5]. Neither patients’ severity nor immunosuppression status modified risk of presenting negative POCST results. Lymphocytes’ count was not significantly different, however; it


Dear Editor,
The severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) pandemic requires accurate diagnostic tests to triage patients between properly isolated and regular wards [1]. Gold-standard tests are based on reversetranscriptase polymerase chain reaction (RT-PCR) performed on nasopharyngeal swabs [2]. Quick serology tests detecting immunoglobulin M and G (respectively IgM and IgG) targeted against SARS-Cov-2 are also available [3,4]; however, concerns have been raised on their sensitivity in intensive care units (ICU), where patients are more severe and some immunosuppressed.
In this multicenter observational study, we assessed sensitivity of a point-of-care serology test (POCST) regarding SARS-Cov-2, in ICU patients presenting severe SARS-Cov-2 infection. All included patients were positive for SARS-Cov-2 using routine RT-PCR methodology. POCST was sampled with finger prick, with 10 μL of blood and tested with the device, BIOSYNEX COVID-19 BSS (IgG/ IgM)® (Biosynex, Illkirch-Graffenstaden, France). Each POCST incorporated a quality control. Concordance between RT-PCR and POCST was assessed regarding the presence of IgM and/or IgG. Patients for whom POCST showed no IgM and no IgG were considered negative. The study was approved by institutional review board (00012608-2020-01) and registered under clinicaltrials.gov identifier NCT04467008.
Overall, 99 patients were included. Patients were 62.4 ± 13.3 years old, 34.7% were women, and average body-mass index (BMI) was 29.1 ± 5.9 kg/m 2 . Mean Simplified Acute Physiological Score II (SAPS II) was 50.1 ± 22.8. Average delay between POCST and first symptoms was 17.9 ± 9.1 days (see baseline characteristics in Table 1). Results were obtained in less than 10 min for all, except in 2 (2.0%) in whom quality control was not met; hence, tests required to be performed twice.
The other three different serology profiles were IgM+/ IgG− in 7, IgM+/IgG+ in 64, and IgM−/IgG+ in 19 patients. Delay between first symptoms and POCST was significantly different across all four groups. Contrary to SAPS II, distribution of age, BMI, and lymphocytes' count did not significantly differ across all four groups (see Fig. 1b-d).
In this observational study in ICU patients, sensitivity of POCST was similar to specifications provided by the manufacturer (93%). Variables associated with negative results were age and delay between onset and POCST which was expected given known dynamics of immunization after SARS-Cov-2 infection [5]. Neither patients' severity nor immunosuppression status modified risk of presenting negative POCST results. Lymphocytes' count was not significantly different, however; it © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.  was twice as lower in false-negative patients although a lack of power be incriminated. Although multicenter, this study suffers from small sample size, hence validation in larger cohorts aiming at assessing effects of POCST on in-hospital virus contamination and beds management may answer whether these quick diagnostic tests alleviate burden of SARS-Cov-2 on ICU beds and staff [6].
To conclude, we assessed diagnostic performance of a point-of-care serology test for SARS-CoV-2 in 99 patients hospitalized in ICU with a definite SARS-Cov-2 and found a 91.9% sensitivity, confounded by younger age and shorter delay since symptoms onset. POCST sensitivity was not considered elevated enough in clinical practice to help triage between SARS-CoV-2 isolated wards and regular ICU wards.