Sometimes a patient’s illness is misdiagnosed or goes undiagnosed.
This is especially the case when the illness is a new one, as in the early days of AIDS or COVID-19.
Once a new illness emerges, tracing a Patient Zero becomes a high priority – but in the meantime, the earliest patients have often died, and no blood samples remain.
Under what circumstances would a patient’s blood sample be retained long-term so that it could be tested later? And how long would such samples be stored? I imagine it’s not practical to retain such samples without a compelling reason.
I don’t know what the rules are now, but i worked as a lab assistant in the 80s and we had a -70 chest freezer full of old plasma samples from people who had had blood tests. As part of some research project i had to fish out a couple dozen of them (they were identified by number) defrost, remove enough to test for something, and return the rest of the sample to the freezer.
I may not have understood what was going on there, but i believed that everyone who’d had blood tests done by that department had the leftover stored in that freezer.
It was in the endocrinology department of a research hospital.
I work for a major private diagnostic lab, but in logistics, not in actual laboratory operations, so I’m not 100% sure on this, but I think my company keeps blood specimens 3-7 days after testing, depending on the type of specimen and the type of tests. It’s just not practical to keep them indefinitely. It takes a lot of room and energy and costs significant money when you’re talking about processing thousands of specimens a day.
Also, important to note, most blood tests have to be performed within a 24-72 hour window. Many have to be performed within a few hours (“STAT” tests). Preserving blood samples beyond those windows doesn’t actually serve any purpose.
On the other hand, many tissue specimens are much more stable. Our pathology lab stores tissue blocks preserved in paraffin for years after the initial testing, and I’ve transported tissue blocks between our lab and other medical facilities that were a year or more old. I’ve seen online references that properly prepared and stored paraffin blocks are stable for decades. I don’t think they’d be particularly useful for retroactive diagnosis of an infectious disease, though.