Contract Manufacturing : COVID-SeroKlir

COVID-SeroKlir, Kantaro SARS-CoV-2 IgG Antibody IVD Kit


Key features

  • Received FDA EUA and CE mark
  • 30,000 COVID-19 patient test data set
  • 97.8% sensitivity and 99.6% specificity
  • Minimises false positives and false negatives
  • Peer reviewed in Nature and Science

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Precise and reliable measurement of COVID-19 IgG antibodies

The Kantaro COVID-SeroKlir kit is a direct ELISA for the quantitative detection of human IgG antibodies to the SARS-CoV-2 virus in serum and plasma (K2-EDTA/Li-Heparin) samples. COVID-SeroKlir has FDA Emergency Use Authorization (EUA) in November 2020 having previously received a CE mark in October 2020.


COVID-SeroKlir has demonstrated 97.8% sensitivity and 99.6% specificity for detecting SARS-CoV-2 specific IgG antibodies against two virus antigens, the full-length spike protein and its receptor-binding domain. COVID-SeroKlir is a two-step enzyme-linked immunosorbent assay (ELISA) and can be used by any certified laboratory* without the need for proprietary equipment. 

The SeroKlir ELISA kit contains components to test 630 patient samples and uses standard ELISA protocols and equipment. The test comprises a two-phase ELISA, the initial plate screens for RBD positive or negative samples and the second plate provides a quantitative result of the antibody titre (concentration) using full length Spike protein.


The SeroKlir ELISA kit was developed by clinicians at the Icahn School of Medicine at Mount Sinai Health System, New York(1). The test has been trialled on a cohort of more than 70,000 patients including over 30,000 who were diagnosed with COVID-19(2).  


*UKAS and ISO 15189 in UK, Rilibak and ISO 15189 in Germany. Equivalent certification required in all other countries.

Kit specifications


Kit component


7 x RBD plates

96 well polystyrene microplate coated with recombinant SARS-CoV-2 Spike protein RBD antigen sufficient for 630 screening tests

3 x spike plates

96 well polystyrene microplate coated with full length recombinant SARS-CoV-2 Spike protein sufficient for 228 quantitative tests


RBD Positive Control
RBD Negative Control
Spike Low Control
Spike Mid Control
Spike High Control


8 calibrators (range 0-200 AU/mL)


RBD conjugate concentrate - IgG ELISA

Spike conjugate concentrate - IgG ELISA

Conjugate buffer - IgG ELISA

Sample buffer - IgG ELISA

TMB substrate - IgG ELISA

Stop solution - IgG ELISA

Wash buffer - IgG ELISA

Product Code:  CVD2-2019

Performance data



Performance specifications

Assay type

Solid phase sandwich ELISA


96 well one-piece plate

Assay length

3.5 hours (RBD ELISA)

3.5 hours (spike ELISA)

Sample types

Serum (20 uL)

EDTA plasma (20 uL)

Heparin plasma (20 uL)

Assay range

3.2 – 160 AU/mL





Peer reviewed & published

We believe that our ELISA method will be very useful for serosurveys aimed at determining the real attack rate and infection fatality rate in different human populations, and to map the kinetics of the antibody response to SARS-CoV-2.

Amanat et al. Nature Medicine, 26 2033-1036 (2020)

We show that titers are relatively stable for at least a period approximating 5 months and that anti-spike binding titers significantly correlate with neutralization of authentic SARS-CoV-2. Our data suggests that more than 90% of seroconverters make detectible neutralizing antibody responses. These titers remain relatively stable for several months after infection.

Wajnberg et al. Science 10.1126/science.abd7728 (2020)


Two phase ELISA interrogating both the full length Spike protein and its Receptor Binding Domain (RBD):

  • RBD used as first phase to identify antibody negative samples
  • Full length Spike protein used in second phase to confirm positive samples and return a quantitative antibody titer

Analytical sensitivity

Analytical sensitivity: Limit of Blank (LoB), Limit of Detection (LoD), and Limit of Quantitation (LoQ) were established according to the recommendations in CLSI guideline EP17-A2. RBD ELISA and Spike ELISA summary data is presented opposite


Positive Percent Agreement: For the positive samples confirmed with a known EUA-authorized molecular test, PPA was 97.8%. Two samples that tested negative with the COVID-SeroKlir Kantaro Quantitative SARS-CoV-2 IgG Antibody Kit also tested negative on an existing EUA approved serology test, suggesting that these were true negative samples.


Negative Percent Agreement: For the negative samples the NPA was 99.6%. There were 14 samples that tested positive on the RBD ELISA. Of these samples, 13 subsequently tested negative on the Spike ELISA. Therefore the number of negative samples was 281 out of 282.


Sensitivity RBD ELISA
0.70 0.82 ---
1.98 2.61 3.20

Clinical utility

An initial qualitative (screening) ELISA is performed against recombinant Receptor Binding Domain (RBD) of SARS-CoV-2. Positive samples from this screen are analysed by a quantitative ELISA against full length SARS-CoV-2 Spike protein. The assay aids in establishing the quantitative levels of neutralizing antibodies indicative of an adaptive immune response to SARS-CoV-2 in patients suspected of previous SARS-CoV-2 infection, or for the detection of IgG seroconversion in patients following known recent SARS-CoV-2 infection.


Determination of the number of individuals who are demonstrated to have developed specific antibodies to SARS-CoV-2 aids in the determination of seroprevalence in any geographic region or group of exposed individuals and may be indicative of the potential risk of reinfection. The results of the assay correlate with the neutralization of SARS-CoV-2 virus in vitro.


Results from the COVID-SeroKlir Kantaro Quantitative SARS-CoV-2 IgG Antibody Kit should not be used as the sole basis for diagnosis and should not be used for the diagnosis of patients with acute COVID-19 infection.

Results are for the detection of SARS-CoV-2 IgG antibodies. IgG antibodies to SARS-CoV-2 generally become detectable at 10-14 days following infection but may occur later. The presence of IgG antibodies, following previously negative testing, defines IgG antibody seroconversion following SARS-CoV-2 infection.


Negative results do not preclude acute SARS-CoV-2 infection and should not be used as the sole basis for patient management decisions. IgG antibodies may not be present for more than two weeks following infection, and patients may remain infectious during acute infection even if IgG antibody is present. Results must be combined with clinical observations, patient history, and epidemiological information. The sensitivity of the COVID-SeroKlir Kantaro Quantitative SARS-CoV-2 IgG Antibody Kit early after infection is unknown.