This is only partially true. Due to things like Henrietta Lacks cells (HeLa cells for those working in cell culture), we actually have informed consent around this. They can’t just use your samples for not consented collection purposes (though in some cases, the further testing may fall under the original consent)

HHS rules note:

“If the tissues are identifiable, then subjects must provide consent for the secondary use and that consent must cover the elements of consent in 21 CFR 50.25.”

That really only applies to healthcare providers covered under FDA and HIPAA regs.

Obligatory not a lawyer etc.