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What Is The Window Period For An ELFA Test?

Posted on Wed, 2 Dec 2015

Question: can one take elfa antigen test as early as 9 days after exposure? how early can one take elfa p24 antigen test

Answered by Dr. Indu Kumar (56 minutes later)

Brief Answer:
9 days is early in your case,there are chances of false negative.

Detailed Answer:
Hello

Enzyme linked fluorescent assay(ELFA) P24 antigen test detects simultaneous both P24 antigen and antibody.This test is used in window period for screening.

Detection of P24 antigen in blood depend upon many factors like individual host response,test used,viral characteristics etc.P24 test is generally only positive from about one week to 3-4 weeks after infection with HIV.

9 days is early in your case,there are chances of false negative.I suggest repeat test after at least 2 weeks of exposure.

Initially HIV RNA appears in blood then antigen and finally antibody appears.

Viral RNA can be detected within first 2 weeks using highly sensitive RT-PCR method,so you can go for it.Otherwise you may wait for one more week.It will be more sensitive.

Test for antibodies after 12 weeks is confirmatory.

Get well soon.
Hope I have answered your query.
Further queries are most welcome.

Take Care
Dr.Indu XXXXXXX

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Indu Kumar (22 hours later)

Sir, thanks for your response. Today(exactly 2 weeks after exposure) I took cmia test for hiv1 and hiv 2 and the result was negative. How sensitive the result would be? Can I relax and stop worrying? Pls advice. This test and date was suggested by the doctor and I was told that I can almost conclude and asked to confirm at 21st day by the doctor. Thanks

Answered by Dr. Indu Kumar (3 hours later)

Brief Answer:
It is nice to hear that tests are negative.You are almost safe.

Detailed Answer:
Hello

It is nice to hear that tests are negative.You are almost safe.
But we can't take chance.As we discussed earlier,production of antigen and antibodies varies with person to person.
This is the reason for repeat test at 3 weeks which almost exclude the chances of infection. CMIA is a combo test and it is almost confirmatory in 3 weeks.

We can extra precaution by testing of HIV 1 and 2 antibodies after completion of 12 weeks.This will be confirmatory as 12 weeks is the maximum limit of production of antibodies.

Don't worry at all.You are almost safe.

Get well soon.
Hope I have answered your query.
Further queries are most welcome.

Take Care
Dr.Indu XXXXXXX

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Indu Kumar (7 hours later)

Thanks a lot doctor. I will do the confirmatory test after 3 weeks and 12 weeks.

Answered by Dr. Indu Kumar (12 hours later)

Brief Answer:
Yes,you should go for tests for 100 % confirmation.

Detailed Answer:
Hello
Sorry for replying late

Yes,you should go for these tests for 100 % confirmation.

Get well soon.
Hope I have answered your query.
Further queries are most welcome.

Take Care
Dr.Indu XXXXXXX

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar