Comment by hombre_fatal
4 hours ago
My girlfriend accidentally told the donation center she went to Mexico, and they banned her from donating for four years.
Apparently you'd only go to Mexico to eat brain tacos and share needles with cows. Surely there's a better way to filter out risky blood.
> Surely there's a better way to filter out risky blood
It's simple Bayesian probability. Blood tests have a relatively high error rate. Hep-B tests have a 6-12% false negative rate early in the disease, and Hep-C is 3-6% even later in the course of the disease. That's considered a "very low" false-negative rate for a blood test.
In Bayesian terms, blood tests don’t “screen” for a disease. They reduce the odds ratio of contaminated blood by a factor of 10 or so. But the ultimate odds still depends heavily on the prior odds—the prevalence of the disease in the donor population: https://en.wikipedia.org/wiki/Prior_probability. Even with testing, you can reduce the risk of contaminated blood by drawing blood from a pool of donors that has lower prevalence rate of diseases.
Yes... travel, tattoos, drug use and sexual behavior can and should disqualify a person from donating blood.
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.
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.
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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.
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With travel, I understand that there is a higher risk of lots of diseases, and testing against all possible infectious diseases is not feasible. Drug use is also obviously disqualifying. But why would you care about someone's sexual behavior? The blood must be tested for common drugs and common blood borne diseases regardless, and it's perfectly possible to engage in sexually risky behaviors and not have any venereal disease (unlike with drug use, where it implicitly means you will have levels of those drugs in your blood), just like it's possible to be very careful with your sexual behavior and still get a disease.
Note: for tattoos, I have no idea if the problem is also related to venereal diseases, or if there is any problem from contamination with the tattoo ink itself, and I don't care enough about this subject to look it up.
> But why would you care about someone's sexual behavior? The blood must be tested for common drugs and common blood borne diseases regardless, and it's perfectly possible to engage in sexually risky behaviors and not have any venereal disease
Men who have sex with men are something like 50-100x more likely than the general population to acquire HIV. HIV tests do not have a 0% false positive. They will not catch all very recent infections. The rationale for excluding them until recently is that it’s defense in depth and it doesn’t hurt the blood supply much because they only make up about 2-3% of the population.
The current rule is that MSM don’t face a blanket ban, but if you’ve had anal sex in the last 3 months you have to wait because anal sex is inherently more likely to transmit HIV and the tests may not catch a very new infection. Other diseases like Hepatitis have a similar issue.
The answer to all of that is mainly hepatitis C, that can have a window detection of 6 months, even more.
And yes, you can be very careful and get a disease. But they are playing statistics here: over 60% of injected drug users have Hep-C, that means a lot of prostitutes. They won't and shouldn't trust anyone who say "hey, I had unsafe sex against all advice, but was very careful with the tattoo in a dark cellar and the heroin party, pinky promise".
Unfortunately tests are not 100% accurate and there's a window between when the pathogen is present and when it's detectible. Add in that many viruses aren't directly detectable, the tests look for antibodies to the virus.
This is why they usually ask if you've had a new sexual partner in the past 3 or 4 months. This is the window period for detecting some STDs and other diseases.
For tattoos, if the artist isn't using a brand new set of needles for you, you risk bloodborne disease transmission, with hepatitis B being a particular danger.
Well, it's the having of an infectious blood borne thing that disqualifies you.
m-m sex is still disqualifying even if all parties are completely clean and safe. it's discriminatory.
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People have more unprotected, regrettable sex during travel and vacations, so maybe they're on to something?
Sounds like something you should test rather that just rely on heuristics
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I don't get the sense we have any standards for actually vetting the blood that's donated, which is deeply concerning
We do test the blood, but they also do coarse grained screenings like this to avoid some level of waste on intake.
We do test the blood, but they also do coarse grained screenings like this to avoid some level of waste on intake. It's like having client and server side validation.
We do, they are just not cheap enough to do on individual donations so you have to throw away a big batch every time they catch something.
I was banned roughly the same time for being in the US. I guess its mostly so they don't need to check for unexpected things.
I get it, just seems like it could be more granular, especially since she could have just said no.
> eat brain tacos
What's wrong with that? Animal brains are a common dish in many countries, including France, Asia, and parts of the United States
Vector for prion disease.
There are other ways she can donate her blood.
"Accidentally"? Implying she should've lied about it even though they probably have some reason (evaluating risk presumably) for asking?
Let's say a year ago, you walked across a bridge in Mexico for five minutes to see if it's true that Mexico has a yellowish haze like in the movies. Oh, it doesn't. Then you walked back to Texas.
A year later, you go to a blood donation center and they ask you: "Did you go to Mexico in the last N years?"
If you say "Yes", you are banned for four years. If you say "No", you donate liters of blood over the next four years.
If you were in this exact situation, how would you weight which answer is better?
Sounds like a wild party.