I have had many questions with regards to the ECLIA test and how it measures up against the ELISA test.
Of course many people are very worried that their tests by ECLIA are not as reliable as the very well studied ELISA test. It’s time to put an end to the mystery once and for all.
Before we even get down to the tests themselves, we have to understand a little about how the human immune system works.
Our bodies do not like anything that is foreign (insert right wing French government joke here). When a virus enters the body, the body recognizes it as foreign and tries to get rid of it.
One whole virus is too much for the body to deal with. It needs specific targets to attack. These specific targets are little bits of protein on the virus called antigens.
The body produces antibodies that are unique and specific to these antigens and act like smart bombs to seek out and kill the virus.
So the presence of an antibody to a particular antigen indicates the presence of the virus.
So far so good?
Let’s not forget that antibodies are also antigens themselves. The antibody is made up of a head that is unique and specific and attaches to a particular antigen and a tail that can be recognized by other antibodies as a foreign antigen.
This fundamental science forms the basis of immuno testing which includes the ELISA and ECLIA tests.
So with all that background, let’s get back to the clinical scenario.
In the 1980s, HIV was finally identified as the pathogen that caused AIDS. The big problem was we needed a way to tell if someone was infected with HIV or not.
The most obvious method was to look for antibodies to HIV in the body.
So the medical profession turned to the ELISA test.
This is how the test was performed (nb: there have been great changes in ELISA technology over the years. For more info, look out for my next post: the different generations of ELISA).
First get a plastic board with a hole in it.
Stick bits of HIV antigen on the walls of this well.
Fill the well up with the patient’s serum.
If the serum contains antibodies to HIV, the antibodies will stick to the antigens on the wall.
The only problem that remains is how do we tell if any antibodies have stuck? Do not forget that these are tiny invisible molecules.
One ingenious method was to make an antibody that we can see and attach it to the antibody that is stuck on the wall of the well. Remember antibodies are antigens too?
The earliest methods made this so-called secondary antibody radioactive so its presence could be detected with a Geiger counter. I guess the scientist figured out real quickly that this wasn’t a really good idea.
Lately, another technique was developed. It involved attaching a chemical to the secondary antibody that would glow when an electrical current was passed through it. And the ECLIA technique was born.
So to answer the question which is more accurate? Well, both tests are inherently really good and theoretically nothing short of genius. However, all medical tests have an inherent inaccuracy. I will discuss this in more details in my next post : the different generations of ELISA.
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