In many cases the clinics do not know which type of test is in use. They will just say it's an antibody test and to test outside the window period.
I asked the health advisor here what type of test they used when they tested me at 28 days. She was a little taken aback I asked and said it was just a normal antibody test.
It was only after I tested outside the window that I found out the test they use is a combined Antibody / P24 Antigen test.
I felt a little more reassured at the validity of my 28 day result from knowing that. It was quite by acident that I presented at 28 days though.
I think many if not most of the GUM clinics in the UK would be using Ab/Ag tests. They have to use Ab/Ag for blood so a lot depends on which processes use the machine. Some larger health authorities may have a machine dedicated for the blood supply and one dedicated for GUM and other Diagnostics e.g. Ante Natal.
The reagents are updated anyway. I was looking on the Biomieriuex site and I couldn't find 3rd gen reagents strips. The 4th gen reagent strips are a drop-in replacement anyway
If a Western Blot is indeterminate the patient will get a call back for another blood draw.
p24 does not detect the virus directly, the p24 antigen is often associated with early seroconversion. Others may cross-react with it that are negative. The western blot is used as a confirmatory test only after a reactive ELISA. The ELISA is often reactive before the WB. Take care.
well does it test for the most common antigens then? I read that the western blot can show up indeterminate for some non-infected individuals so is the ELISA more specific than the western blot or what, coz they do the elisa first I think and only a western blot to confirm if the elisa reacts.
Also how many copies of the virus can they detect?
p24 is only prevalent in the first couple weeks to a month and a half or so