Understanding your Roche Anti-SARS-CoV-2 (Nucleocapsid) test result

This article explains the result from the Roche Anti-SARS-CoV-2 (N) test to give Testing For All users a better understanding of how this diagnostic test works. The test is designed to give a “positive” or “negative” answer to the detection of antibodies to the Nucleocapsid protein, which is generated by the body to fight off the SARS-CoV-2 virus (the Nucleocapsid is the pink shell in the illustration above). Research from public health bodies around the world, and the dataset generated by Testing For All users gives useful context and insight into the result that you have received from our COVID-19 Home Total Antibody Test.

To help you interpret the result, please find some statistics.

  • We saw an overall positive rate of 13.3% for those who decided to take the test in October and September 2020
  • Results range from 0.000 to 223.6 for the first 6000 tests completed 
  • The Roche test gives a numeric count as the output from the analyser, which is the machine that runs the test. In simple terms a count of less than 1.0 means that antibodies were not detected, and greater than or equal to 1.0 means antibodies were detected. Please note that in the test instructions, Roche claim that the magnitude of the measured result above the cut-off is not indicative of the total amount of antibody present in the sample. However, the table below gives you further insight into the spread of results.
Result Type Numeric Count Number of Samples
Negative – Antibodies not found Between 0 and 0.128 5,278
Between 0.128 and 1 193
Positive – Antibodies found Between 1 and 10 218
Between 10 and 100 449
Between 100 and 200 155
More than 200 16

If you have taken the test, you can see your numeric count at https://testingforall.app/results

This information is provided to help you understand if your result is clearly positive or clearly negative or if you are potentially in a borderline area. The test is designed to give you a clear positive or negative result but we believe it is important to understand both how close your result is to the cut off index value of 1.0, and where it sits in the context to other results. You can see that the majority of negative results were in the range 0 to 0.128. In the excellent Public Health England report Evaluation of sensitivity and specificity of four commercially available SARS-CoV-2 antibody immunoassays the authors suggested that reducing the numeric count at which you were considered positive to be greater or equal to 0.128 would improve the ability of this test to return true positives as positive, without a significant increase in false positives. From a Testing For All point of view we believe that if you have a numeric count of 0.128 to 1 you may have had some immune response and therefore been exposed to SARS-CoV-2 but we think it makes sense for you as an individual and Roche to take a careful stance and set the cut off for antibody detection conservatively as a numeric count of greater or equal to 1.0.

There is no strong evidence yet to suggest that those who are proven to have had the virus, and to have produced antibodies are immune to reinfection, or becoming an asymptomatic carrier. Triggering an immune response measured by the creation of antibodies and through T cell response is the primary method by which the 170+ vaccines under development around the world would provide protection.

My negative numeric count is the same as my friend’s numeric count. Is this right?

A large number of negative numeric counts are 0.05, 0.06, 0.07 or 0.08. To give you a better understanding in September 2020 approximately 8% of all numeric counts are 0.05, 23% are 0.06, 36% are 0.07 and 5% are 0.08. For this reason, those that are negative will often have the same result. It is much less likely for those who are positive to have the same numeric count.

My numeric count is greater than 0. Does it mean I have some antibodies?

No. A small numeric count above 0 (ie. 0.05 or 0.09) means no antibodies were detected.

This article attempts to explain simply how the sophisticated analytical diagnostic returns its results. For further reading on research related to anti-SARS-CoV-2 antibodies please see the following links:

Coronavirus antibody tests: what we know so far by The Crick’s George Kassiotis

Immune responses and immunity to SARS-CoV-2  by the European Centre for Disease Prevention and Control

James Monico
Co-Founder, Testing For All