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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.

 

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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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138 Comments

  1. I had a low risk exposure where a small amount of blood from a patient mouth was dripped to my 3 old days wound at the back of my wrist (no scab). The blood was from a hiv+ person due to his teeth fallen out. I tested negative after 45 days using ECLIA. Will it turned positive at 3 months?

    • Add: The patient claimed and showed me his viral load test. 20 copies/ml that was done on 2/2/2017 and my incident happened at 29/11/2017

    • I believe your tests are as good as conclusive, given your risk is very low.

      • im a dental student and was exposed to blood of a HIV+ patient. Here’s what exactly happened. Its was 29/11/2017, i assisted my clinical partner on dental extraction of a carious tooth. We were both wearing gloves and other universal precaution. During the extraction, my gloves was exposed to the blood and i had to deglove to take something out of my pocket. After about 2-3 minute i re-use the glove back again. What i didnt realize is that i had 3 days old abrasion wound at my wrist that was caused from playing basketball. The wound is about 2mm in size. It was not bleeding but was still quite pinkish showing the flesh and maybe i was scrapping the scab formed. I am afraid during deglove i might have touched the wound because the flove was kinda big for my size

        The patient only had told us that he was HIV+ one week after the extraction and i was freaking out because of the wound. he also showed a report of his viral load being 20 copies/ml that was done on february 2017. I then had headaches and 1 unexplained sore at the side of my tounge that healed about 3-4 days. I then tested negative hiv 1/2 at 6 weeks (45 days) after the incident at a hospital setting where they collect blood from my vein and they also tested all other thing from my blood. It was ECLIA HIV test.

        After 7 weeks i developed a flu and fever and was relieved with Paracetamol but the nasal congestion had not resolve and i also develop some productive cough that is getting better. And i had 1 weird raised non itchy rash on my chest that healed after 1 week. Plus i also had some weird reddish slight raised thingy on my penis head, about 1 or 2 but was not painful. Recently the penis rash/breach cause soliggt discomfort. Im planning to get tested at 3 months mark and really worried that it might turned positive after having experienced these symptoms. Im having a strong symptoms, the congested nose is still present even with usage of loratadine

        Can you please assess my risk and is my 6 week negative test going to change at 3 months mark? Thanks in advance

      • Jenglot1717

        But i have rash that is slightly raise non itchy on my shoulder. And my penis head has a slight raised thingy. Im in a monogamous relationship, but sonetimes i dont wash my penis after sex. Could that be the reason to my penis lesion? Also after 8 weeks of the exposure i got a 2 day fever that resolved with PCM but runny nose persist for about 10 days. Should i go and retest?

  2. haiii doctor,

    I already test 55day rapid test 4generations 93day full blood test(ECLIA),120day rapid test 4generations…my question form you experience any case came positive for next test.. doctor please answer my question..

  3. “Let’s not forget that antibodies are also antigens themselves” does it mean our body produce the p24 antigen too? or our body doesn’t produce p24 antigen?

  4. please dr..I do not understand one answers from dr tan…please you tell about it…..

    The increase in counts is due to antibody cross reaction and has nothing to do with whether you have HIV or not.
    please dr.please dr.please

  5. Kirikou

    Happy New Year Doctor,

    I had protected sex with a girl I met in a bar. While penetrating her (vaginal) the condom broke I stopped everything (maybe 30 seconds in her vagina). I waited and washes my penis. Afterwards she asked to put another condom and continue but I was no longer in the mood. This is the history of actions taken:
    – Condom broke on the 19th of Nov. 2017
    – I did an Ab HIV 1/2 It came out Negative on the 27th day post exposition (15 Dec. 2017)
    – I did a Chemiluminescence Siemebs Centaur XPT test on the 34th day post exposition (it was negative with the Hiv Indice at 0.07).
    – I did another ECLIA Roche Test on the 31 Dec. 2017 (43 days or 6 weeks post exposition) It came out negative with the ratio E/S 0.45 (below 0.9).
    – I recalled that I did a routine check at the same laboratory in July 2017 and ratio E/S was just 0.17

    Please does it mean that the level of Antibodies are increasing in my blood?

    If I do another test in 2 weeks could that ratio be over the 0.9 threshold???

    Many Thanks for your reply

  6. hai doctor

    I had sex with sex worker at bali.

    I tested by 4generations rapid test at 53day after risk(negative)

    I test by 4generations rapid test 93day and lab test eclia (negative)

    I’m concerned about HIV 2

    are my test conclusive??

    do I need further testing??

    is 6months testing required??

    • please replay doc,

      from doc experience any case test 3months negative and next test become positive

    • Your tests are conclusive. They would include testing for HIV-2 antibodies. I do not believe you require any further HIV testing.

  7. Hi! My name is rako from indonesia, my last unprotected sex was January 2017, after few weeks l see single sore look like molluscum contagiosum until now ,
    I took Rapid ICT test 7 August 2017
    Rapid Immunochromatographic (ICT) test and result was non-reactive
    Still . I got worried. After one test of
    non reactive results.
    Pls advice me, of what to do? how accurate was this test.
    Thank you!

  8. stalin1812

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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

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