3rd generation HIV Test vs 4th generation HIV Test

A lot of people do not quite know what’s the difference between 3rd generation vs 4th generation HIV Test Kit. How HIV tests work Third generation HIV tests (ELISA antibody) When you become infected with HIV, your body will start to produce specific antibodies (proteins that attach to the virus to try and destroy it). […]

A lot of people do not quite know what’s the difference between 3rd generation vs 4th generation HIV Test Kit.

How HIV tests work

Third generation HIV tests (ELISA antibody)

When you become infected with HIV, your body will start to produce specific antibodies (proteins that attach to the virus to try and destroy it). An HIV antibody test looks for these antibodies in your blood, saliva or urine. If these antibodies are found, it means you are infected with HIV. This test is only accurate after three months, because this is how long it takes your body to produce enough antibodies for it to show up in a test.

However, First Response HIV Test Kit says you can test after 3 to 4 weeks of exposure. While in my own opinion, to be on the safer side, do a retest after 3 months, 6th month and 1 year later. You will get a lot of opinions from internet though.


**90 days is the usual safety window period for HIV antibodies test (which checks ONLY for antibodies and NOT for P24 antigen).


Fourth generation HIV tests (ELISA combined antigen/antibody)

Fourth generation tests look for HIV antibodies, but also for something called p24 antigens. The p24 antigens are part of HIV itself, so you have a lot of these in your blood in the first few weeks after infection. This is why you are most infectious to others in this period too. Fourth generation tests can detect (p24 HIV viral protein) from 11 days to 1 month after you have been infected.

[We all already know that the HIV antibody test becomes quite reliable at 4 weeks and as good as conclusive at 6 weeks. Although most health authorities still recommend a 3 months window period. So putting these 2 tests together gives you a very powerful tool to diagnose HIV infection in as little as 3 weeks. When the level of P24 antigen peaks in the blood gives us maximum accuracy.]

Note: The 4th generation HIV test is also known as DUO or COMBO because it looks for hiv 1/2 antibodies, and also the p24 antigen. The p24 antigen is only present in the first two or three weeks. Once enough antibodies start to be produced, the p24 antigen disappears.

**P24 antigen is usually detectable by 28 days, the time when antibodies may still be not detectable. So DUO will check for both antibodies and P24 Antigen and hence will help in possible earlier diagnosis of HIV at the time when antigen will be detectable, but not the antibodies. Once the antibodies start producing, P24 antigen will usually start disappearing and again as DUO will also check for antibodies so it will also be again helpful that time. That is why it is also called Sandwich test.


HIV test What do they test for? What is the window period? How long for the results? Reliability
Third generation antibody tests HIV antibodies 3 months  Between 1 to 7 days High
Fourth generation antibody & P24 antigen tests HIV antibodies and p24 viral proteins (antigens) 11 days – 1 month Between a few days and a few weeks High

 So What’s the difference between these 3rd and 4th generation?

The median detection time was demonstrated to be 7 days earlier (range 0 to 20 days) compared to 3rd generation enzyme immunoassay antibody tests. Meaning you don’t have to wait too long to get the results. As for the pricing, 4th generation will be more expensive compare to 3rd generation.

**Fourth generation tests have been widely used in Europe for many years, although a handful of clinics, still use third generation despite current guidelines.

About HIV Seroconversion

(…HIV seroconversion is the time in which a person first develops antibodies for HIV. They will not yet test positive on an HIV antibody test. The word just means that your sero status is converting from being HIV antibody negative to HIV antibody positive)

Research shows that 97 percent of people will have produced enough antibodies to accurately test positive within three months. Sometimes, it takes people as long as six months to test positive, but this is rare.

Because everyone’s window period is different — and because the tests are different — it’s recommended that you test before the three month mark, you get re-tested for HIV after three months if you got a negative test result at first. Or, people who are exposed to HIV frequently may prefer to get tested with increased regularly — say, every few months.


What about “delayed Seroconversion” which is rare case?…

The CDC website states

” Most people will develop detectable antibodies within 2 to 8 weeks (the average is 25 days).Therefore, if the initial negative HIV test was conducted within the first 3 months after possible exposure, repeat testing should be considered >3 months after the exposure occurred to account for the possibility of a false-negative result. Ninety-seven percent of persons will develop antibodies in the first 3 months following the time of their infection. In very rare cases, it can take up to 6 months to develop antibodies to HIV”


What doctors says about this “rare delayed Seroconversion”, what causes this to happen…

It is extremely rare for a person to take any longer then 6 months to develop detectable antibodies.

In case a individuals have conditions that result in late production of antibodies – testing after 12 weeks or after 6 months is advised. Most of these conditions are rare genetic diseases – and do present much earlier in life and individuals will always be sick with respiratory and diarrheal infections throughout their life.

Such disorders include :

1. Disorders of antibody production: Hypogammaglobulinemia ; X-linked agammaglobulinemia ; IgA deficiency ; IgG deficiency ; IgM deficiency ; Hyper IgM syndrome ; Wiskott-Aldrich syndrome • Hyper-IgE syndrome

2. Common variable immunodeficiency

3. Cell-mediated (T) : Di George’s syndrome ; Purine nucleoside phosphorylase deficiency
Severe combined (B+T) x-linked: X-SCID ; Adenosine deaminase deficiency

4. Conditions resulting in : Leukopenia, Lymphocytopenia , Idiopathic CD4+ lymphocytopenia

5. Complement deficiency

“Your tests doe at 4 months post exposure, might be conclusive.”


So What DO YOU THINK? How often should you re-test HIV Test Kit?