N-protein presents early in blood, dried blood and saliva during asymptomatic and symptomatic SARS-CoV-2 infection

Abstract

The COVID-19 pandemic continues to have an unprecedented impact on societies and economies worldwide. There remains an ongoing need for high-performance SARS-CoV-2 tests which may be broadly deployed for infection monitoring. Here we report a highly sensitive single molecule array (Simoa) immunoassay in development for detection of SARS-CoV-2 nucleocapsid protein (N-protein) in venous and capillary blood and saliva. In all matrices in the studies conducted to date we observe >98% negative percent agreement and >90% positive percent agreement with molecular testing for days 1–7 in symptomatic, asymptomatic, and pre-symptomatic PCR+ individuals. N-protein load decreases as anti-SARS-CoV-2 spike-IgG increases, and N-protein levels correlate with RT-PCR Ct-values in saliva, and between matched saliva and capillary blood samples. This Simoa SARS-CoV-2 N-protein assay effectively detects SARS-CoV-2 infection via measurement of antigen levels in blood or saliva, using non-invasive, swab-independent collection methods, offering potential for at home and point of care sample collection.

Reduced Relative Sensitivity of the Elecsys SARS-CoV-2 Antigen Assay in Saliva Compared to Nasopharyngeal Swabs

“…Our results show a clear advantage of NPS as a specimen in combination with the probed antigen test. This is in concordance with other antigen test systems which, in general, have shown lower sensitivity compared to NPS [ 35 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ]. One of the automated antigen tests previously evaluated for saliva samples is the Lumipulse G SARS-CoV-2 Ag assay, a chemiluminescent enzyme immunoassay which received the CE marking for qualitative and quantitative detection of the SARS-CoV-2 N antigen on both saliva and NPS samples.…”

“…Another automated antigen test evaluated for saliva is the Simoa SARS-CoV-2 N Protein Antigen Test, which is an EUA for the qualitative detection of the N antigen from SARS-CoV-2 in NPS specimens. PPA and NPA of this assay with molecular testing were 92.3% and 98.1% (N = 26) for days 1–7 [ 53 ]. Thus, compared to these two SARS-CoV-2 antigen assays, the Elecsys Anti-SARS-CoV-2 Antigen assay has a lower sensitivity but higher specificity.…”

“…As we showed, conducting head-to-head comparisons of NPS and saliva for both PCR and antigen test is critical to dissect if matrix effects in saliva exist. As only few studies have assessed saliva in the context of SARS-CoV-2 antigen tests, and those that have, recorded variable results [ 35 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ], it can currently not be excluded that antigen tests generally show a reduced sensitivity across diverse tests systems. Alternatively, these effects may be test-dependent and can be modest enough to allow application in mass testing as a recent study suggests [ 41 ].…”

Volumetric Absorptive Microsampling: Its Use in Covid-19 Research and Testing

“…With several studies demonstrating the role that plasma viremia has on COVID-19, and its possible predictor of mortality [ 18 , 35 , 36 ], D Shan and team embarked on developing a sensitive direct antigen test to measure the viral NC protein for both dried blood Mitra microsamples and also saliva [ 37 ]. Comparing to nasopharyngeal PCR, their assays showed >90% PPA for SARS-CoV-2 positive patients, and >98% negative percent agreement, for all matrices within a week of a PCR+ test.…”

Hemofiltration with the Seraph® 100 Microbind® Affinity filter decreases SARS-CoV-2 nucleocapsid protein in critically ill COVID-19 patients

“…The nucleocapsid protein (N-protein) of SARS-CoV-2 is a structural protein that oligomerizes to form a complex surrounding viral RNA, thus protecting it from the host cell environment. It is abundantly expressed within infected cells, where it facilitates viral RNA transcription, an essential step for viral replication Recently an ultrasensitive Simoa ® immunoassay has been described that robustly measures SARS-CoV-2 N-protein in venous blood, dried blood microsamples, and saliva [ 1 ]. This study measured N-protein in longitudinal blood samples of COVID-19 patients and demonstrated readily detectable viral antigen two weeks after initial positive PCR testing, with concentrations gradually decreasing, inversely correlated with anti-SARS-CoV2 adaptive immune response.…”