It is not logical that the test
personnel would re-use the same capillary
tube to test
consecutive patients. And if for some reason that happened, absence of visible blood is a strong indication that there was insufficient contamination to transmit HIV.
You're not going to be the first person in the world in over 20 years to catch HIV through a testing procedure.
For any more information or discussion, you'll have to re-post your question in the HIV Prevention and Safe Sex forum.