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One Confusion

Does anyone have an idea why blood banks use a 21-22 day window period in case they are using ELISA to deem the blood safe in comparison to 3 month waiting period for conclusive hiv testing?
I am aware that a lot of blood banks now use NAAT for testing along with P24 antigen test but still a lot of places wordwise use only ELISA as it is cheaper and cost 4-5 dollars per blood donation.
14 Responses
Avatar universal
Most all blood banks use NAT testing. If they get a positive result they pitch the unit. Contact the blood bank in your area and ask about their policy.
Avatar universal
yes, for the blood banks using NAT, the window period they follow is 11 days. What, I am trying to stress here was that still a lot of places in the world do not use NAT for screening blood supply and use ELISA for screening purposes at 21-22 days. If the blood donation does not show reactivity to hiv by then, the blood is deemed HIV free. US also followed similar guidelines till 1995/1996. Only beyiond that they introduced the P24 component in testing which further cut their window to 16 days.

So, what I find confusing is that if blood banks to confidently rule out HIV infection using ELISA at 22 days, why is 3 month conclusive test period set for testing in scenarios post exposure(sexual, needle stick).

Also, there are a lot of developing countries spread across Europe, Asia and Africa which still use ELISA as screening test in blood banks. Moreover, NAT cuts down the infection detection period by only 11 days.

Any insight????
Avatar universal
Have you ever looked into all the testings blood banks do before making a unit of blood available for transfusion?
Avatar universal
Whatever I know is not 1st hand information. I know they test for Hepatitis, HIV for sure and maybe few other communicable diseases but there are plenty of official documents present on the web which keep on stating that the window period they use is 21-22 days when using ELISA.
And, moreover, had I been sure, I would not have asked this question. But, from what I read as a first hand transcript mentioned on many official websites, it does seem that wehn blood banks use NAT, the blood is deemed free of infection after a window period of 11 days for HIV and when they use ELISA, the blood is considered hiv free after 22 days.

Correct me if I am wrong
Avatar universal
The ELISA is not the only test used. Nor does a unit of blood go by one testing. A unit of blood goes through multiples of repeated testing before it can be used. You need to go to the blood banks sites and read about their testing procedures.
Avatar universal
Can’t they test the blood before passing it on?
There is no available test that completely removes the ‘window period’ where someone
has HIV in their blood which won’t show up in tests. It is true that serum testing can
give a quicker result than antibody testing but whether the window period lasts for one
week or 12 weeks it still exists and still presents a risk. Serum testing is also much more
expensive than antibody testing, which is still the test used by the Blood Service in
Not all blood products can be heat treated to kill off viruses that they may contain.
It is also important to remember that blood is still pooled and one donation is usually
shared amongst several recipients. It should also be remembered that the recipients are
unlikely to know that they are at risk until after they have potentially infected others.
The Blood Service freely admits that no test is perfect and that mistakes can be made in
the laboratory. Taking blood from populations who are at low risk of having HIV reduces
the number of infected donations that could be missed by testing which is why filtering
takes place before donations are given.

This is published in october 2007 from terrence higgins trust
219662 tn?1223858560
I personally don't understand your question.  The blood banks don't use any window period, not 3 weeks and not 3 months.  In the US, they ask a donor to wait a year after any high-risk activity.  People at the highest risk for HIV (gay men, IVDU, CSWs) are deferred from giving blood for a lifetime.
Avatar universal
" In the US, they ask a donor to wait a year after any high-risk activity.  People at the highest risk for HIV (gay men, IVDU, CSWs) are deferred from giving blood for a lifetime."

Everyone is not honest about exposures and US is not the only country in the world. My question is pretty simple. A lot of blood banks especially in developing countries use HIV ELISA for screening and dedicatedly follow the 21-22 day window period guideline for detecting the infection. If no infection is detected during that period of time, the blood is considered safe for further usage.

In US, most of the blood banks use NAT which cuts window for infection detection to 11 days.

Now my confusion stems from the fact that majority of blood banks across the world give all clear to donated blood after a window of 21-22 days on the basis of ELISA, then why is window period still set to 3 months.

Another interesting aspect - Also, practically there is no way for the blood banks to figure out whether the person is lying or not about his/her exposure in preceding weeks. How do they know that they are performing NAT at 11 days or ELISA at 22 days after exposure. The blood specimen is valid at the day and time of the draw. You can not store blood for 22 days post donation and consider the test done 22 days post donation a test that will necessarily cover up the minimal diagnostic window of 21 days.

Avatar universal
In the US a unit of blood is tested again just before it is given out for a transfusion.
Avatar universal
The blood can be tested 5 million times after donation but the infection detection ability within the unit of donated blood remains the same as the day the blood is donated. The day of donation could be a year post exposure or could be 10 days post exposure. What I am asking is that other than trusting the donor's word about his last possible risky exposure, do blood banks have any other choice??

There will not be any difference in the NAT results or antibody results conducted on the same specimen of the blood if the test done is 1 day post donation or if it is done after storing it for 22 days post donation.

Avatar universal
Laboratory testing of donated blood

RISK OF ACQUIRING VIRAL ILLNESS FROM A TRANSFUSION — Safety measures, such as improved screening tests, have dramatically reduced the risk of acquiring a viral illness from a blood transfusion. Recent estimates suggest the following risks of developing certain infections after receiving a unit of blood:

One in 250,000 for hepatitis B
One in 1.9 million for hepatitis C
One in 2.1 million for human immunodeficiency virus (HIV)
One in 2 million for human T-cell lymphoma/leukemia virus (HTLV)

It's up to you danny_grey if you take a chance on a transfusion or dieing from not getting one.
Avatar universal
You are right. I just thought tis was a very interesting aspect worth a discussion because truly there is no way in which blood supply could be 100% safe. These guidelines of blood donation are guided by individualistic ethics and morals and US still stands way ahead on those basis as a result of minimum basic education but similar things can not be said about lot of developing countries where education levels still suffer.
219662 tn?1223858560
Well, I still disagree, or maybe don't understand your query.  A blood bank does not go by any window period calculation, not 3 weeks or 3 months.  What they do is the only thing that they can do - give people out a questionnaire and give every unit a test.  Of course people could be lying.  A person could have gay sex and show up to give blood a week later, lie on the questionnaire and be allowed to donate.  Such things have happened and people have been infected this way.  What other option can a blood bank have?  You can't get the police to investigate everyone who shows up to give blood, that is not feasible.  They just have to live with taking a risk.  Nobody ever claims blood transfusions to be 100% safe.

The good news is that testing is very accurate these days.  NAT technology in particular makes it almost impossible for HIV transmission to take place, 1-in-2 million odds cited by Teak is correct.  Infected people that are in the NAT-window period are practically not infectious.
219662 tn?1223858560
"Now my confusion stems from the fact that majority of blood banks across the world give all clear to donated blood after a window of 21-22 days on the basis of ELISA, then why is window period still set to 3 months."

What are the blood banks that give the all clear after 22 days?  I don't know of any.  If there was an emergency shortage in the blood supply, they might revise the guidelines a bit.  For example, there is talk of allowing the CSW to donate, as long as they haven't done it in the last 12 months.  There is also a push to allow gay men to donate, but that is unlikely to happen soon
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