Decoding antibody testing – Why you could have Covid and not know it

Antibodies are small proteins which your body produces when it is fighting off an infection. The purpose of an antibody test is to screen for the presence of antibodies in your blood. If you contract Covid-19, your body will produce antibodies, the same way it does when you have a cold, or when you are vaccinated. The purpose of the test is not to check for the virus, but rather to see if your immune system has responded. BizNews talks to Dr Noluthando Nematswerani about antibodies, and the current limitations of antibody testing in South Africa. – Claire Badenhorst.Dr Noluthando Nematswerani is the head of clinical policy with Discovery who's been keeping her eye on antibodies. Antibodies are not very well understood amongst the general population. Maybe you can tell us why it's so important in the whole development of these vaccines that at some point in time antibodies are created and what they are..___STEADY_PAYWALL___.So, antibodies are released by the body – it's an immune response – so we call them your fighting cells. When you are infected or exposed to any infection, then your body will release these antibodies. They call on the army, the rest of the army in your body to fight against the infection. There are various antibodies, some are early on in the infection..The one that is very important there is the IgM. So, if we test for antibodies and we pick up that IgM is elevated, then it almost reflects that you have been recently infected. And then there's the other antibodies that almost appear two weeks later after the infection has almost subsided in most cases. It's almost like memory for future infections. So, when we test your person and we find that they've got IgG antibodies, then we know that they have been previously infected by that particular virus or bacteria or whichever infection we're referring to..The importance of antibodies is that they do confer immunity going forward. So, the presence of these neutralising antibodies we know actually are very good in killing off the virus. What research has been focusing on, therefore, is to look at the quality and the amount of these antibodies to actually see if those who have been infected have got sufficient amounts of antibodies, and also the quality that we're looking for, so that, if you are exposed to future infections, you are able to fight..Read also: How far are we from a trustworthy Covid-19 vaccine in SA?.Here in South Africa, we were talking off air about some developments on this front. Perhaps you could share those with us..So, I think that the developments are around the antibody testing itself. So, I think we are aware that the currently available tests in South Africa for the diagnosis of Covid-19 are the RT-PCR. We call them molecular tests; they are in the diagnostic area and they look at viral particles, and once they've tested for it, they can say the person definitely does have, or does not have the infection. We do know that they are not 100% accurate, but they are relatively, quite sensitive..So, when we look at test kits, we look at two aspects. We look at its sensitivity, meaning, if I test you, the likelihood of me picking you up as an infected case, and then the specificity which says if you do not have the disease, the likelihood of me excluding the disease. So, we need test kits that are highly sensitive and highly specific. We know that the currently available tests are highly specific and I mean highly sensitive, even though they're not 100% specific..We know that antibodies only develop a week later after you've been infected. So, from seven to 10 days and onwards. So, it means you can be acutely ill and I can test you using an antibody test, and I may still tell you that you are not infected because I'm looking for antibodies that don't usually present early on in the infection. So, those are some of the limitations..There's been a lot of excitement around antibody test kits, and some people refer to them as rapid test kits, because most of them, you know, the results, you can get them in 10 to 15 minutes. So, people are really looking for quick turnaround times. And also, you know, they are cheaper from a cost point of view, and also it is not as uncomfortable. It's just a finger prick. Now, in South Africa on Friday, our regulatory authority released some approval for some of these tests to be used in our local labs – not to be used at home, at present. But it does appear that this has been retracted – the approval..Why did the authorities, the regulatory authorities, withdraw that permission? What's the story behind that?.From what we understand, because we do need the national guidance, firstly, before you can introduce test kits into the environment, because otherwise then there's inappropriate use and then it actually does not serve the purpose that they are intended for. They say they had actually approved them in error, but there's also the issue around the fact that, and I think it's just the timing. I think they will eventually approve these test kits, but we do need to have the guidance in place for them to actually then be properly used..And from Discovery's perspective, once the approval is given, will you be encouraging greater use of the test kits?.Firstly, our approach is that, with these test kits, we will consider them for funding. If they are somehow approved, so they must get regulatory authorisation. Secondly, they must be validated in our local setting. We must know that they are doing what they are meant to be doing. And secondly, they must fit in within our national guidelines..Right now they don't have a major role in diagnosing the infection, so we are thinking that most funding should be limited to day to day until we can actually find clinical utility in the management of Covid. And by clinical utility, I mean that, if the results are really going to impact clinical management of that patient, then we would then consider funding it within that Covid benefit. But for now, there are quite significant limitations in terms of the positioning. We just need to understand how it's going to play out in our environment..Read also: Mailbox: Herd immunity must be why Covid-19 is on the wane in Cape Town – doctor.So, those people who've gone for antibody testing and have come back with strong antibodies telling them they've had Covid, they don't necessarily have to relax now and stop wearing masks?.Oh, definitely not. Definitely not. And also, I think it's very important to just understand. So, I spoke about sensitivity and specificity earlier on..It's important for us to understand that some of these, they may be highly sensitive and highly specific, but because of the timing of the infection, if you're wanting to use them for diagnosis, they will give you a false negative result, meaning that you have the infection but they tell you you don't have the infection. But there's another aspect of it where they may also say you've got the infection when you actually do not have the infection..The reason for that is because you're looking at antibodies to coronaviruses, and some of them may not be specific to SARS-CoV-2. So, remember there are other coronaviruses that are responsible for the common cold. We call that cross-reactivity where you might actually be labelled as Covid-positive when you actually just have antibodies for, you know, from other coronavirus infections that you might have had. So, they are not perfect, but I think the ones that are being evaluated for registration in our country are highly specific and highly sensitive, but they still have limitations..And the other important thing is that some of these test kits you know, they'll tell you you've got antibodies, but they don't tell you about the quality of the antibodies. You might not have neutralising antibodies, meaning that if you are, you know, exposed, you can still be infected. Those are some of the things I think people should be aware of. Yes, you know, it's always tempting when it's a quick thing, you know, 15 minutes and I have got my result, but what do you do with that result is what some of us are more concerned about rather than just having a test result..It sounds almost as though you shouldn't even be taking the antibody testing because there's so many downsides to it. .I think for me, a person should only do this with the guidance of a health care professional and there must be a clear reason and understanding of what their test results are going to mean. Because if you've got a result that could be wrong, that could be right, you just need to know how to interpret that, and what are you going to use that information for?.Then I think people need to just be educated and I think these are some of the reasons why we come on these platforms, to actually share some of this information so that people are informed. When you've got an antibody test result and it says it's positive, can you safely say it's really accurate, and also if it says you are negative, can you rule out infection, and definitely not.