Reliable detection

Independent studies from Italy confirm a reliable and accurate detection of anti-SARS-CoV-2 IgM and IgG antibodies ^{[1, 2]}. Positive results were confirmed using RT PCR. Of particular note is the high positive rate for IgG detection in patients with known start of symptoms especially in the early (<5 days) and middle (5‑10 days) stages after the appearance of symptoms.

Table 1: Rate of positivitiy of the different methods in the 48 patients in whom the date of symptom onset was available. 
 

Symptom onset	Euroimmun		Maglumi
	IgA	IgG	IgM	IgG
5 days	1 / 30 (3.3%)	0 / 30 (0%)	1 / 30 (3.3%)	1 / 30 (10%)
> 5-10 days	4 / 13 (30.8%)	2 / 13 (15.4%)	2 / 13 (15.4%)	7 / 13 (53.8%)
> 10-21 days	5 / 5 (100%)	5 / 5 (100%)	3 / 5 (60%)	5 / 5 (100%)

^{Giuseppe Lippi et al. 2020}

High reproducibility

The study by Padoan et al. ^[2] confirms the previously published, very good analytical performance of the Maglumi system, and the 2019-nCoV IgM and IgG chemiluminescence immunoassays. This is very important for measuring the course of IgG so that even small titer changes can be detected reliably. The kinetics of antibody occurrence in COVID-19 patients was also confirmed.

High specifity for accurate results

A commonly known problem in diagnostics is a lack of specifity when using (too) sensitive methods, leading to false-positive results. Especially when diagnosing SARS-CoV-2, attention should be paid to the reliability and accuracy of the obtained results. An independent study from Belgium attested an impressive 100-% specifity (n = 198) for the IgM and IgG antibody tests supplied by medac ^[3].

The importance of specifity is illustrated by the following example. In a case where a positive result was obtained for IgA only but not IgG as the marker for an infection of the recent past a low specifity of the IgA test causes difficulties in the interpretation of the diagnosis.

EC-compliant validation of the tests

The anti-SARS-CoV-2 IgG and IgM antibody tests were successfully validated in compliance with the criteria set out by the European Commission (EC) in April 2020 ^[4].

Consequently, the antibody tests were investigated respectively concerning the following interferences:
 

• Endogenous influences: Haemoglobin, bilirubin, triglycerides, rheumatoid factor and HAMA
• Interaction with the following medicinal products: Acetaminophen, acetylcysteine, adefovir, ampicillin sodium, Aspirin, cefoxitin, entecavir, ibuprofen, lamivudine, metronidazole, rifampin, telbivudine, tetracycline and theophylline

Exclusion of cross-reactions

Based on the tests of different kit batches, cross-reactions with the following related human coronaviruses can be excluded for the IgG and IgM antibody tests ^{[5, 6]}:
 

• HCoV-HKU1
• HCoV-OC43
• HCoV-NL63
• HCoV-229E

^1. Giuseppe Lippi, Gian Luca Salvagno, Manuela Pegoraro, Valentina Militello, Cecilia Caloi, Angelo Peretti, et al. Assessment of immune response to SARS-CoV-2 with fully automated MAGLUMI 2019-nCoV IgG and IgM chemiluminescence immunoassays. Clin Chem Lab Med 2020

^2. Andrea Padoan, Chiara Cosma, Laura Sciacovelli, Diego Faggian and Mario Plebani Analytical performances of a Chemiluminescence immunoassay for SARS-CoV-2 IgM/IgG and antibody kinetics. Clin Chem Lab Med 2020

^3. Isabel Montesinos, Damien Grusonb, Benoit Kabambac, Hafid Dahmaa, Sigi Van den Wijngaerta, Soleimani Rezac, et al. Evaluation of two automated and three rapid lateral flow immunoassays for the detection of anti-SARS-CoV-2 antibodies. J Clin Virol. 128 (2020)

^4. Current performance of COVID-19 test methods and devices and proposed performance criteria. Working document of Commission services, Europ. Commission, 16 April 2020

^5. 2019-nCoV IgG (CLIA) test kit, Report of cross-reaction with human coronaviru

^6. 2019-nCoV IgM (CLIA) test kit, Report of cross-reaction with human coronaviru