[MCOH-EH] HIV 4th gen positive, Western blot negative

Swift, Melanie melanie.swift at Vanderbilt.Edu
Wed Jul 2 11:10:45 PDT 2014

Jeff, the 4th generation HIV test screens both for p24 antigen and for HIV-1 and 2 antibodies. So a positive could be due to antibody OR antigen. The 4th gen test picks up new infections when you only have antigen and no Ab yet. So diagnosis is maybe 2 - 3 weeks earlier. 

There is an algorithm recommended for the confirmation testing process, attached.
(NAAT stands for Nucleic Acid Amplification Test - the viral load UCSF was talking about.)

BTW if you use this type of HIV test for your exposure followup testing, you can simplify the f/u regimen to baseline, 6 weeks and 4 months.

Hope this helps,
Melanie Swift, MD
Director, Vanderbilt Occupational Health Clinic

-----Original Message-----
From: MCOH-EH [mailto:mcoh-eh-bounces at mylist.net] On Behalf Of Jeff Jacobs, MD
Sent: Tuesday, July 01, 2014 9:24 PM
To: mcoh-eh at mylist.net
Subject: [MCOH-EH] HIV 4th gen positive, Western blot negative

Our hospital switched to the 4th gen HIV Ab/Ag test about 1 year ago and I encountered the following situation a few days ago. 

We saw an employee that was bitten by a source that had blood in their mouth. Source SBFE panel was negative for all (HIV, Hep B and Hep C) but the employee's baseline HIV Ab/Ag test was positive. A Western blot came back a day later and that was negative. The employee denied use of iV drugs and seems like a pretty health-conscious guy, for what that's worth. The only other abnormality on his labs were elevated AST/ALTs but again he denied alcohol use. I'm seeing him back early next week and have spoken with him a few times about this situation, most recently today at our clinic. 

I spoke to the UCSF PEPline and they suggested that we draw an HIV viral load PCR soon and re-test the 4th generation HIV test in 3-4 weeks on the employee. Their concern is that sometimes the 4th generation test picks up recent HIV infection sooner than the Western blot and they felt that this process would rule that out. Interested in your thoughts. Thanks. Jeff

Jeffrey A Jacobs, MD, MPH
Medical Director
Einstein LiveWell EHS
1303 Tabor Rd
Philadelphia, PA 19141
FAX: 215-456-1840

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