I wonder if a vitamin supplement contains 50mcg biotin per serving will affect my 4th generation hiv test?

Welcome to our Forum.  Thanks for your questions.  The biotin issue is rather confusing.  50 mcg of biotin will not have any impact whatsoever on the accuracy of your  4th generation test for HIV.  You could take 10 times that much and there is no theoretical interference.   You should have no problem.   EWH---

Thank you, Dr Hook. I didn't have any sexual activities for 2 or 3 years. The 4th generation hiv test I took yesterday was all negative. Am I completely safe from Hiv? Is there any other vitamin other than biotin may interfere with the result (I don't take any medicine for now but I took vitamin supplements.

Thanks for the additional information.  Your results are absolutely conclusive.  There are no supplements which would interfere with the reliability of your tests.  ---

When I did the test yesterday, the nurse first tried to get blood from my right arm, but it was unsuccessful. He then remove the butterfly needle from my right arm and put it in the tray. I saw a small amount of blood in the soft tube connect to the needle. I asked the nurse about it twice but he said he just opened the package of a brand new needle and the blood is from my right arm, so I am fine. I trusted him and let him get blood from my left arm. However, when I got home I started to worry about the needle. I afraid that the nurse reused the needle, and the blood I saw is not from me. I talked with my doctor who ordered me the test. He said they never reuse needle, so I have zero chance of getting any infection, but I still worried about it.

I think you are worrying needlessly.  Needles of the sort you describe are not reused.  I suspect the nurse went through your vein, resulting in the small amount of blood you describe.  ---