[lemontea88]

This is a question which I got from USMLE Rx which I got it wrong and I do not agree with the answer, maybe cuz I got my concepts wrong?

32-year old woman, has Pneumocystis jiroveci infection. Physician suspects patient may have HIV. WHich of the following lab techniques could determine if patient has HIV infection?

A) Northern blot
B) Southern blot
C) Western blot
D) PCR
E) RFLP

Answer was Western blot. But shouldn't PCR be a much better test?

 

[khanar]

I think it should be reverse transcriptase PCR not PCR to pick up HIV
but am not sure

 

[khanar]

First of all I do agree with GNND85 that HIV being an RNA virus it needs RT-PCR not regular PCR.
But I don't think that's the reason the answer is wrong.
They wanted to tell you that in clinical practice we start with a cheaper more practical option which is either ELISA or Western blot specially if the case can be diagnosed by such techniques (as opposed to a newborn of HIV positive mother or recent exposure like needle stick for example).

Second, USMLERx usually explains each and every option, so what did they say about the PCR choice!

Third, USMLERx is know to have several "wrong" questions and that's why they put a feedback with each question and you can send them feedback about that question.

 

[sak2114]

The screening tests for HIV are antibody tests: ELISA confirmed by Western Blot. The Reverse Transcrpitase PCR is only used in special circumstances: 1. for infants of HIV positive mothers (antibodies screening is not helpful here). 2. for accidental needle prick of healthcare workers.

 

[lemontea88]

Ahh I see.

Regarding what did they say bout the wrong option, I don't remember the exact explanation, but bascially, that question wasn't explained well in Rx.