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Comment by vablings | Hacker News Reader

All of these things can mostly be tested. When I donated regularly in the UK after being in the southern US, they screen me for west nile virus but still take my blood and use it.

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The UK also has a wait time for many countries including Mexico.

https://my.blood.co.uk/eligibility/travel/article?id=47&titl...

Granted it’s shorter, but there are longer wait periods depending on the country. It’s defense in depth because false negatives happen and some viruses take time to show up on tests.

"If you spent over 4 weeks in primitive or rural accommodation you have to wait for 4 months after your return before giving blood. However, if you were travelling and staying in places which are modern and clean, such as typical tourist areas, please wait 4 weeks from your return due to Tropical Virus risk which includes Chik V, Dengue or Zika risk providing you do not have symptoms of these."

Not quite the four years.

The first paragraph is

“ If you visited the rural areas of the states - Chiapas, Chihuahua, Durango, Sinaloa districts, Quintana Roo, you need to wait for 4 months after your return to the UK before giving blood. ”

The US rules also aren’t 4 years (not sure why someone told the OP that). It’s 3 years after undergoing malaria treatment. And 3 months after visiting a malaria prone area.

https://www.redcrossblood.org/faq.html#eligibility-travel

Blood is tested for disease, but the false negative rate for each test is its own risk.

If you got blood from an addict living on the street engaging in prostitution and tested it, would you trust that blood?

I wouldn't.

The bigger worry isn't really false negatives, modern PCR based testing is incredibly good. There is always risk but it's frankly extremely low. The bigger issue is that blood is pooled before testing to make that powerful testing economical. If you increase the rate at which you get (also possibly false) positives you risk having to throw out whole batches of pooled donations.

The false negative rate for HIV testing in newly infected people is actually pretty high, like 50% within the first few months high.

No, it's not though. That's true for antibody tests commonly used for individuals because it's cheap. The window period for nucleic acid testing that is used for blood supply is very short. This test is similar to what's used to confirm a positive antibody test, but isn't used for individual testing because it is too expensive. Hence the pooling.

The UK had mad cow eons ago, and that's still a risk factor for giving blood in some places.

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