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HIV ELISA test and HIV ECLIA test

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.

Another technique involved attaching an enzyme to the secondary antibody. This enzyme causes a color change when a color substrate is added. And thus the ELISA test was born.

 

 

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.

 

advise


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About Dr. Tan
Dr. Tan graduated from the National University of Singapore in 2001. His residency was in the two largest public hospitals in Singapore; Tan Tock Seng Hospital and Singapore General Hospital.

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118 Comments

  1. stalin1812

    if hiv ECLIA test will be conclusive after one month?
    2) the result of non reactive in Elisa mode test depend which generation?

  2. Is eclia Elisa test? Does labrotary test with Elisa good in 8 week? I think 3. Generation. And l want to ask about plasma/serum test we use. Sometimes l Touch the pad with bleeding finger. It has got recombinant hiv antigens And antibodies. Are they infectious ?thanks for Your help.

  3. anxious 0.347

    Question: 
    Hi I went to get HIV test done as I was anxious of exposure during blood donations done by me before and the person .Who was doing the test took me to lab where two to three testing strips were kept and they were already having blood samples of previous visitors . He took a pin meant for piercing and he peirced me with that. And while doing so I closed my eyes to take pain . and he took a strip to collect the blood on it . and he wiped the strip to collect the blood on it . while doing .So my eyes were still closed .Only I was able to feel what he was doing later the test came negative . but after hours I got doubt how sure that he had used the new strip . what if ererroneously he had used the strip which was having blood drawn from other person . hence hence exactly after 4 weeks I went to another private lab to get the screening done there they did eclia test and it came negative . but here I have many questions like . here they took the blodd from the other hand than from the previous test . the test report was stating that reference range is 0.90 and mine was .0.235. They say less than 0.90 is non reactive . and again after 15 days i got the same eclia test done this time it was 0.347 and they said iys negetive . but why that 0.235 and 0.347 why that range has increased by 0.11 . and is this fluctuation with in the cut off reference range is common or is it increasing trend . I am literally having sleep less nights please help me out I am fed up with going to labs and getting tested . is it common for normal persons . and is the test results vary depending on the body part from where the blood is drawn. Please let me know what is the common reference range for normal person in eclia test(not Elisa). Do I need to get tested again . please suggest considering that first HIV test with those strips as exposure and test taken after 6 week as conclusive .though there was increase in results between 4th and 6the week. As both are with in reference range.and a normal person with out any exposure will have this fluctuations or will he be 0 or less when measured in eclia

    • Dr Justin Sim

      Really? You believe he just erroneously used the same strip as the guy before you? Firstly that would be stupid becuase he is risking everything as a healthcare professional. Secondly a used strip won’t be able to collect any more blood. He would be wiping and wiping and wiping but nothing would soak because it already is soaked with someone elses blood – so you see this makes no sense!! You need to get tested at 1 month or 3 months depending on the type of test you use to be conclusive. Forget about the absolute number as there is always cross reaction – the important thing is that the number is less than the positive range.

  4. WorriedMalaysian

    Hi doctor,

    I received unprotected oral sex and protected vagina sex from a CSW 100 days ago. I never had any symptoms except for a 3 days period of gastroenteritis infection on the 90th-93rd day of exposure. I recovered after taking medicine prescribed by my GP.

    I did two test in total. One on the 67th days (HIV Ag/Ab Combo (CMIA) – nonreactive) and another on the 99th days (HIV 1 and 2 Ag/Ab ECLIA – not detected).

    Can I move on and resume unprotected sex with my wife?

    Your advise is higly appreciated.

    Thanks.

  5. Worries

    I have my usual Employee Screening test and they tested ECLIA- the result revealed 1210 COI ( positive)

    Please help me to fully underatand

    • Dr Justin Sim

      I cannot interpret this test for you. You need to ask the doctor who did this test for you.

Trackbacks/Pingbacks

  1. HIV – Understanding the Window Period | GP Services - […] testing techniques and technology. There are now multiple different tests for HIV including ELISA, ECLIA, CMIA, Rapid Tests, Western Blot,…
  2. Medicines to Prevent HIV – PEP and PrEP | HIV - […] HIV ELISA and ECLIA test […]

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