Info on Understanding a COVID Anti-body Tests.

The SARS-CoV2 Ab Nucleocapsid test looks for whether you have been previously naturally infected with Covid. Positive means a person has been infected. Negative means they have not.

The SARS-CoV2- Semi-quant Total Ab (“Spike Antibody”) shows whether there has been a response to the vaccine or an infection.  NOTE: Prior to May 8, 2021 the maximal response showing antibodies was >250. The maximal response is now >2500 or 10x more specific.

  • If the Semi-quant Total Ab number is <0.80*, there was no response. 
  • If you have not been infected with Covid (Nucleocapsid test is negative) and/or your testing was done prior to receiving any vaccine, we would expect your Sars-Cov2- Semi-quant Total Ab to be non-reactive or a value of <0.40.
  • If the Semi-Quantitative Total Ab number is >0.70*, there was a response to the vaccine, The maximum value for a response is >2500. The value of 2500 is clearly greater than >0.81. Nevertheless, both patients would be considered positive. While the greater the number, the more antibodies were detected, at this time we do not fully understand if the low positive value indicates less protection from infection compared to the highest value.
  • If the number for Semi-quant Total Ab is noting a response and your Nucleocapsid test was positive, we cannot say for sure whether your Spike response was based on the infection or the vaccine.
  • If the number for Semi-quant Total Ab is >0.80 and your Nucleocapsid test was negative, we can assume your Spike response was based on the vaccine.
  • If you are in your vaccine journey, your result may change based on you receiving your final vaccine dose.
  • If your testing was done 3-5 weeks after your final vaccine dose your Sars-Cov2- Semi-quant Total Ab is unlikely to change with a repeat test. However, our study is planned to perform follow up testing three to six months after your final vaccine, as this will help us determine the persistence of antibodies if you produce antibodies initially. We will contact you when is the right time for this additional test.
  • If your Sars-Cov2- Semi-quant Total Ab is <0.40, going forward we will be considering asking people who fall into this category to have a follow up study in looking at T-cell response which is another way the body creates immunity and responds to the vaccine. This will be a research test requiring an invitation and consent.

In the event your Spike antibody test is negative, we urge you to consult your physician and continue to follow CDC guidelines that specify masking, social distancing, and hand washing. We also urge you to have household members vaccinated.  The true interpretation of the antibody test will become known over time as we learn the association between these results and the chances of infection in the future. LLS is working with more than 20 scientist and clinicians across the USA and Britain with expertise in blood cancer to evaluate the immune response and association with any possible future infections. We value your contribution to this critical work.

There are many reasons why a person with blood cancer may not respond to the vaccine. These may include the type of blood cancer diagnosis and/or current treatments that may are currently or have been given.

We are interested in monitoring vaccine response during the coming months and may be in touch with you 3-6 months from your final vaccine date to have a repeat test performed. There are other ways the immune system can be activated by the vaccine and these have not been tested in the assays that have just been performed. The other assays, such a T-cell response, will be considered in the very near future.

Please share the results with your doctors and as we always recommend, wear a mask, wash your hands, and socially distance.

Should you have questions, please send an email to

*The reason for the apparent discrepancy reported on the LabCorp lab slip of a negative results <0.8 and a positive result of >0.7 is that the actual specific numbers should be < or = 0.79 and > or = to 0.79. The lab reports that the cannot format the numbers in this way so convert to the nearest whole integer.

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