False Negative HIV ELISA test
I have been pondering whether or not to write this article for a long time.
I finally decided to do it in the name of scientific truth and complete transparency.
What I do not want to happen is for this article to feed the unreasonable fear and paranoia that is already out there.
I want to state categorically that I still believe the HIV Combo test is 100% conclusive at 28 days post exposure and the HIV 3rd Gen ELISA Antibody test is 100% conclusive at 3 months post exposure.Click here for more info on the HIV testing Window Period.
Note that the cases mentioned in this article are extremely rare, literally 1 in a million.
With all that in mind, let’s get into the topic proper.
In the 1980’s when HIV was first discovered, we needed a way to determine if a patient was infected with HIV or not.
Out of this need was born the first generation ELISA test which tested for the presence of HIV specific antibodies in the blood. Over the years, these ELISA tests became more and more accurate. However, they all depended on one thing: the assumption that a patient who is infected with HIV will develop antibodies to HIV so that it can be detected in the first place.Click here for more info on the Different Generations of ELISA tests
It was soon discovered that this was not always a valid assumption. There were instances where a person was infected with HIV but yet the ELISA test showed that he was not. This so called ‘False Negative’ ELISA test was initially blamed on the HIV Testing Window Period – the time from when a person is infected with HIV to when antibodies to HIV become detectable in the blood. However, we soon discovered that there were other, albeit extremely rare, causes of a False Negative HIV ELISA test.
The commonest cause of a False Negative ELISA – the testing Window Period
Initially, all cases of false positive ELISA tests were blamed on the testing window period. Till today, testing within the window period is still the commonest cause of a false negative ELISA.
The newer generation ELISAs can detect IgM antibodies which are produced much earlier than the IgG antibodies detected by older generation ELISA tests. This has significantly brought down the window period but it still hovers between 6 weeks to 3 months.Click here for more info on the HIV testing Window Period.
Newer tests including the P24 and RNA PCR has made the testing Window Period even shorter. Furthermore, these 2 tests are not dependent on the presence of antibodies and therefore will still be positive in people infected with HIV but do not develop antibodies (sero-negative infections).Click here for more info on the HIV Combo test Click here for more info on the HIV PCR test
Non-Clade B HIV virus
Once the issue with the testing window period was worked out, another problem arose.
As most tests were developed in North America and Europe, most of the focus was on detecting Clade B viruses which were the most commonly found subtype in these areas.
As such, some HIV ELISA tests that were developed were not so sensitive in detecting non-Clade B viruses.
This problem was quickly picked up and nowadays, HIV tests are all designed to detect non-Clade B viruses.
This is an extremely rare cause of sero-negative HIV infection (i.e. infected with HIV but with no detectable antibodies in the blood).
Hypogammaglobulinaemia in itself is a very rare condition in which patients have a (frequently genetically induced) inability to develop antibodies. It is rarer still to find such a patient and infected with HIV.
To date, I know of only 1 reported case in the NEJM in 2005.
Sero-reversion in End-Stage AIDS
We all know that HIV destroys the immune system and eventually leads to AIDS.
At the very late stages of AIDS, the patient’s immune system may be so poor that he/she is unable to produce antibodies anymore.
The antibodies that were present in the blood then disappear. This is what we call sero-reversion (the disappearance of antibodies) as opposed to sero-conversion (the appearance of antibodies).
Patients in these situations are always extremely ill and the diagnosis of a HIV infection is made by RNA PCR viral load test.Click here for more info on the HIV PCR test
Interestingly enough, when some of these patients are given HAART, their immune system comes back to life and they start producing antibodies again, leading to sero-conversion and positive ELISA tests.
Sero-reversion with HAART
Many people also ask about and are worried about sero-reversion with HAART.
This is extremely rare. There are 2 known case reports of such a phenomenon. This refers to months on HAART and should not be confused with PEP. So far, there have been no case reports of delayed sero-conversion or sero-reversion with PEP.
HIV and Hepatitis C Co-Infection
Co-infection with Hepatitis C can prolong the HIV testing window period up to 12 months.Click here for more info on the effect of Hep C co-infection on the HIV testing window period
Unknown – Sero-Negative HIV Infections
This is what science cannot explain.
There are a group of people in this world, albeit extremely rare, who seem apparently normal in all ways but just do not develop antibodies against HIV when infected with HIV.
These people often progress rapidly into AIDS and are only diagnosed when they are in AIDS stage.
It is theorized that the problem is with the patients rather than the virus. This is because a genetically identical virus in a different patient can illicit an antibody response. In other words, if the same virus infects 2 different people, one will develop antibodies against it and not the other.
It has been theorized that this has something to do with the HLA make up of a person which determines how his/her immune system works. But to date, we do not really know what causes these patients to remain persistently sero-negative.
Although such cases has been described, they are very rare. Less than 1 in a million of HIV cases diagnosed.
How do we overcome this problem?
That is the golden question.
Unfortunately, many of these patients present in late stage AIDS because their diagnosis of a HIV infection has been missed all this while.
The 2 solutions we have are:
- P24 testing or Combo Test
These patients who do not develop antibodies against HIV will have a persistently high P24 level in their blood. So doing a P24 test will identify the infection.
This is very inline with the new HIV diagnostic testing Guidelines published in June 2014 by the US CDC which states that everyone should get a Combo test and not just an antibody test.Click here for more info on the HIV Combo test
- RNA PCR (Viral Load) Testing
These patients who do not develop antibodies against HIV will have a very high HIV viral load. Often greater than 100,000 copies per ml.
There are 2 drawbacks with this test in Singapore:
- It is expensive ($600 to $700) in most clinics
- It cannot be done anonymously
There are cases of people in this world who get infected with HIV but do not develop any antibodies. They therefore have persistently false negative ELISA tests.
These cases are very very rare.
There is no reason for you to doubt the ELISA tests that you have done. If your doctor tells you that your tests are conclusive and you do not have HIV, please accept that happy fact and move on.
If you cannot let go and require that added measure of reassurance, get a P24 test and/or an RNA PCR test.
If you still cannot let go, it is more likely you need psychological help rather than virological help.Click here to see the full range of our HIV/STD Services
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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.