DrVirgo
Forum Hero
Topics: 1096
Posts: 3,515
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Hi Everyone:
Here are my notes for HIV Detection:
Please comment, correct, or add anything I missed.
Thanks.
HIV Detection:
First do ELISA as a screening test: (very sensitive, lots of FP, so Decreased PPV)
A)if it's negative....>
-Person not infected if no risk factors for HIV.
-If reported high risk, can do PCR for HIV virus.
B)if it's positive ELISA (for p24 Ab IgG)....> confirm it with Western blot (very specific; ELISA + WB: PPV > 99%):
...(1) if the test is positive (detect IgG Ab to at least to 2 of these 3 Ags: p24, gp41, gp120 considered positive): the patient is HIV+
...(2) if the test is negative (NO reaction): the patient not infected
...(3) but! if the result of test is intermediate (any reaction that not considered + e.g. if we detect only 1 out of 3 Ab) then 2options:
......>I) Retest in 6mo by western blot: if negative: not infected
-, ......>II) use PCR as a confirmatory test: if negative: not infected.
In general if your patient is HIV negative but has risk factors, retest in 3-6mo
Also:
-ELISA is a screening test
-Western Blot is a confirmatory test
-PCR is the most expensive test
-Antibodies for HIV may not show up until weeks or months after exposure which ELISA and WB cannot detect. PCR can detect HIV at earlier stages because the viral nucleic acid is present immediately upon exposure. It is used to detect HIV in newborns with HIV + mothers.
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| pearljam59
Forum Guru
Topics: 120
Posts: 273
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If you want to test a neonate born to a known HIV mother what assay would you use?!
You cannot test for anti-HIV ABs because the mother passively transmits them to the baby thru the placenta. Therefore ALL babies born to HIV positive mothers will be positive for anti-HIV ABs.
So use PCR to detect the genome of the HIV!
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