Good questions, Wendy. The last thing patients need is to become infected from a blood transfusion, but the possibility is real, if small. I wonder what each of our doctors would say about the idea of getting tested, if not regularly, at least occasionally.
For those who are interested, here is some background information about blood safety:
HIV and other viruses have incubation times during which they aren't detected by tests of donated blood. The Red Cross has tested for the HIV-antibody since 1985 and the HIV antigen since 1996, as part of the blood screening it does.
Potential blood donors are interviewed to try to screen out donors likely to have diseases that may not be detectable. Donors are given multiple confidential ways to opt-out from having their blood used, both before and after making a donation.
That leaves a small risk of getting HIV-infected blood from a transfusion. How small? As of last year, the American Association of Blood Banks (AABB) puts the odds of HIV infection from a one-unit transfusion at between 1 in 450,000 and 1 in 676,000. For comparison, the risk of hepatitis B is 1 in 63,000 and the risk of hepatitis C is 1 in 103,000, i.e., 5 to 10 times more likely. See Infectious Risks.
Tests performed on donated blood continue to improve. Nucleic acid amplification testing (NAT) has been in use in the U.S. since 1999 and has further decreased the chances of HIV in the blood supply.
Interviews also help screen for risk of "mad cow disease" (bovine spongiform encephalopathy, or BSE) and the related disease vCJD (variant Creutzfeldt-Jakob disease). See the Red Cross Mad Cow Disease FAQ.
To Wendy's questions we can add another question: Do our hospitals use donor screening and blood tests similar to those the Red Cross uses?