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With the exception of blood type O-, humans simply can't be given "any old blood type" without the potential of causing serious harm. I assume that in reality, a newly-dead body would still react negatively to an attempt to give the wrong blood type (which might be done in an attempt to resuscitate the body).

Therefore, would death release Vampires from the blood type restriction, or would they also be restricted in what blood type they can consume?

Please note that this previous question asked if there would be a nutritional difference. That is not what I'm asking (and I agree with the answer).

Background

Curiously, science doesn't completely understand how vampire bats metabolize blood. However, they do know that it involves using a plasminogen activator in their saliva (which we have in our blood to prevent coagulation). (source). Beyond this, it appears that vampire bats metabolize blood in the same way all other foods are metabolized.

What do they do with that blood, anyway?

OK, after having some fun reading up on the history of vampires in fiction, and not to invalidate existing answers, or to deny my deepest respect for the Marvel comic universe, I've decided to go with the (obviously obvious) belief that Vampires have ichor in their veins. Therefore, blood is ingested only for nutrition and is not directly conveyed into the bloodstream.

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closed as primarily opinion-based by Aify, Mołot, sphennings, AngelPray, SPavel Jan 5 '18 at 16:46

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ POB - completely depends on your vampires and how/what reason they metabolize blood for. $\endgroup$ – Aify Jan 4 '18 at 21:44
  • $\begingroup$ @Aify Hmmm... that's a good question and actually on point for why this question was asked. Give me a few minutes. $\endgroup$ – JBH Jan 4 '18 at 21:47
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    $\begingroup$ Depends upon how vampires derive power from the blood. Some stories have vampires where the blood of their victims runs through their veins. Some stories blood is required for magic reasons. Others assume that it's just a food source that is digested like normal. $\endgroup$ – sphennings Jan 4 '18 at 21:47
  • $\begingroup$ @Aify, I've edited for metabolism, but let me ask you more about the reason. Would the reason for the need for blood make a difference when it comes to blood compatibility? Would you be suggesting that the reason (e.g., a virus) might itself change the need for blood compatibility? $\endgroup$ – JBH Jan 4 '18 at 21:56
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    $\begingroup$ Are you saying that in your world vampirism is a virus? $\endgroup$ – sphennings Jan 4 '18 at 21:59
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Only if they aren't digesting it

Blood types must be considered in a blood transfusion to avoid rejection by the recipient's immune system. However, if a vampire, or human for that matter, were to drink human blood the stomach acids and digestive enzymes would destroy all of the proteins involved in a blood type before they ever entered the blood stream. If your vampires consume blood in the same way a vampire bat does then they will not need to concern themselves with the blood type of their victims.

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    $\begingroup$ I'd add that a vampire probably has no inmune system at all to be concerned about, to start with. $\endgroup$ – Rekesoft Jan 5 '18 at 11:54
  • $\begingroup$ @Rekesoft And why’s that? Given the reality-check tag, vampires absolutely have an immune system, no question. $\endgroup$ – Konrad Rudolph Jan 5 '18 at 12:12
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    $\begingroup$ @KonradRudolph probably because they’re dead...? They have no heartbeat, body warmth, no brainwaves etc. Why would they have an immune system? How would they - a key part of our immune system is raising body temperature, which a vampire cannot do... $\endgroup$ – Tim Jan 5 '18 at 13:28
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    $\begingroup$ @Tim With no way to fend off bacteria and parasites, their body will decay rapidly. Even under favorable conditions they'd be a skeleton within a few months at most. $\endgroup$ – AJMansfield Jan 5 '18 at 13:33
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    $\begingroup$ @AJMansfield with no body heat they’d struggle to metabolise at a similar rate to mammals, and yet they have no body temperature. With no heart beat, whatever is in their veins doesn’t move. I don’t see why we suspend disbelief for the heartbeat but not the immune system? $\endgroup$ – Tim Jan 5 '18 at 13:35
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Vampire lore is a mess of contradictions and it makes sense to identify how a vampire 'works' in order to provide a more detailed answer to this question. For instance, the fact that they're (in a word) dead, cold and either immortal or extremely long lived indicates a very slow metabolism. On the other hand, super healing capabilities would indicate a very fast metabolism.

In a previous answer I pointed out that excess oxidisation is actually likely to cause faster ageing than not; free radicals are the enemy to a prolonged life.

So; in this answer I'm going to assume that;

1) Vampires do have incredibly slow metabolisms
2) Super healing is either a myth they promote or a result of excess handwavium in their systems.

With that in mind, vampires would digest blood, meaning they break it down for nutrients, making the blood type irrelevant. The reason that they need blood (and blood only) is that the haemoglobin contains just enough oxygen to metabolise the nutrition in the blood, and no more. There's probably no other food type that contains sufficient oxygen to allow the food to be absorbed directly without additional O2 being supplied, which is why;

1) The blood has to be fresh to work (common vampire lore)
2) They bite their victims and intake blood through the mouth
3) Other foods appear as 'toxic' to them (they can't metabolise it)
4) They can survive on such small amounts of 'food'

What all this means is that vampires don't breathe. When you stop and think about it, that actually makes sense. They're dead and they can survive in coffins or underground for extended periods. Some lore also has them able to survive underwater, but if you go to the Dracula book by Bram Stoker, they can't cross running water at all which would be another contradiction. Suffice it to say, that our vampires don't breathe so need oxygen in their food to metabolise it (hence fresh blood).

If we disregard Bram Stoker again (who tells us vampires can survive daylight but with curtailed abilities) and go with the regular lore that vampires are destroyed by sunlight, this is also consistent. Low energy creatures such as vampires would find the relative heat of the day to be overpowering by comparison to their normal very low body temperatures. Assuming they're still warm blooded in nature (in this case meaning that they have to maintain a differential between the outside temp and their internally consistent body temp) then standing in daylight when their normal core temp is so low would be like us standing in the middle of a forest fire and trying to survive. They probably wouldn't burst into flame, but they would die of heat stress pretty quickly.

With all this in mind, I'm going to say that if my understanding of vampire physiology is correct, blood type wouldn't matter to a vampire, but relative freshness would. That means that artificial blood, or even blood stored in a blood bank, would be useless to a vampire. Ideally, they'd want blood fresh from a living artery (going between the lungs and heart of a live animal) so as to be able to metabolise the blood through digestion-like processes that combine the oxidisation step in situ.

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  • $\begingroup$ Vampires can't cross running water not because they'd suffocate but because their skin can't regenerate without any real metabolism and becomes so fragile even a stream of water can do serious damage. A water hose would be devastating to the creature. Slowly sinking into a lake is fine, but leaving it on their own accord might prove painful. $\endgroup$ – John Dvorak Jan 4 '18 at 23:06
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    $\begingroup$ I can't see why the vampires couldn't take oxygen from air. Even if they have degenerated lungs, they can swallow. $\endgroup$ – John Dvorak Jan 4 '18 at 23:10
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    $\begingroup$ Swallowing food and gulping for air are actually two different things. In vampires, you wouldn't want to be able to breathe because that would by definition accelerate your metabolism beyond the body's degraded capacity through massive amounts of excess O2. Besides, this description is an attempt to put a scientific slant on vampire lore, not build a better vampire. If they could breathe, it would make it far more difficult to explain how and why they can only consume blood. This should be read as a conjecture piece that finds one scientifically consistent interpretation of vampire lore. $\endgroup$ – Tim B II Jan 4 '18 at 23:24
  • $\begingroup$ Low-energy creatures that exhibit superhuman strength and some versions metamorphose in seconds, frankly really? Your proposed vampires wouldn't be much of a threat. Having tinkered up various biological vampirism, I'm well aware how easy it is generate new contradictions in doing so. It's fun to play the conjecture game. Plus one for a good try. $\endgroup$ – a4android Jan 5 '18 at 0:52
  • $\begingroup$ @a4android; yep, I was waiting for that. Truth is, that's why vampires cannot exist; too much of their lore is a contradiction that would be scientifically inconsistent which is what I was trying to say in the first paragraph. All good scientific conjecture can do is explain part of it because so much is already contradictory. Thanks for the +1 though. :) If you have already played with this, I'd like to know what you came up with. This answer represents all of about 10 mins worth of thinking effort, not months or more that others may have applied. $\endgroup$ – Tim B II Jan 5 '18 at 1:07
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Reasonable perhaps but completely unnecessary. Let's forget all this modern twaddle about trying to justify the existence of vampires and possible biological mechanisms for how they function and manifest themselves. Steer clear of viral agents being responsible for vampirism. It's time to go to basics.

Vampires are supernatural monsters pure and simple. They are undead. They're already dead. presumably then it is some supernatural force makes them mobile, active, and able to harm the living. The drinking blood business simply comes with territory. Like being allergic garlic, holy water, not reflecting in mirrors (now just try and explain that scientifically, you smart scientifically minded and obsessed kiddy-winkies), and being unable to bear the sight of the Cross. Plus having stakes driven through your heart.

Supernatural forces always work their own perverse, irrational logic. Otherwise what would be the point of them being supernatural forces. Next thing they could be explained scientifically if they weren't.

Presumably the fanging of victims and ingesting their blood might have something with vital spirits or forces, but that a hopelessly outmoded and discredited concept from old-fashioned, pre-modern bad science. Therefore, it could be perfectly in keeping with the operation of supernatural forces and powers.

Let's face with vampires are not only dead, they're most definitely undead. This means there is absolutely no way that mixing blood types or being restricted to specific blood groups makes any sense at all. Why? because they're already dead. They can't be harmed by ingestion of the wrong blood (if that means anything in this context) which is one of the advantages of being dead.

In conclusion, there is absolutely no reason why vampires, supernatural vampires that is, should be restricted in the blood groups of the blood they imbibe and ingest. They are above and beyond any normal physiological or biological functions

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    $\begingroup$ Going by the notion that magic works by its own irrational logic the blood type of the victim could be a factor, just not for any discernable reason. Scientists can figure out why vampires only target certain people but the answer is even more perplexing than the question, as they study magic the more they learn the less sense it makes. People with O type blood are significantly more likely to be twins, and twins are more likely to be born at a certain time of year, and people born on that day are more likely to be gingers, and so on and so forth down the rabbit hole of nonsense we go. $\endgroup$ – Cognisant Jan 5 '18 at 5:26
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    $\begingroup$ @Cognisant That seems reasonable in its own irrational way. $\endgroup$ – a4android Jan 5 '18 at 5:37
  • $\begingroup$ Too reasonable actually a blood type and likelihood of being twins could be due to something genetic, instead it should be something like "they always get a religious symbol on their 13th birthday" and then it turns out that these religious symbols are only from certain religions and that those religious all have literature containing a nonsensical quote and that quote somehow correlates to Pi. $\endgroup$ – Cognisant Jan 5 '18 at 5:49
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Having read the other answers on here, I've come up with an idea.

Perhaps rather than only being able to drink only O- blood, your vampires can only drink one blood type at a time.

This could be achieved by having a dedicated blood sac in the vampire's body, or if you're cool with the vampires not eating normal food, the stomach works too. Most blood types don't mix, and a few days worth of blood is ideally stored in the sac/stomach at any one time. This is going to make feeding difficult, as your vampire can't feed from a conflicting blood type without projectile vomiting afterwards.

Now unless your vampires can smell, taste, or otherwise determine blood type without stealing their donor card, it's going to be a LOT safer to just simply drink O- blood as that can mix with any blood type with no issues.

However, how do the vampires tell who is O- if that is the case? Perhaps they are the ones that are marked by other vampires as prime feeding targets, or maybe vampires would go to the trouble of stealing a list or cracking a database of O- donors!

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  • $\begingroup$ While technically not an answer to the question, it is a GREAT idea! Thanks for the insight! $\endgroup$ – JBH Jan 6 '18 at 0:05
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    $\begingroup$ Maybe they have some tools like mosquitoes. "There's also evidence that one blood type (O) attracts mosquitoes more than others. One study found that in a controlled setting, mosquitoes landed on people with Type O blood nearly twice as often as those with Type A. People with Type B blood fell somewhere in the middle of this itchy spectrum" $\endgroup$ – Mohammed Joraid Sep 4 '18 at 0:58
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    $\begingroup$ "Additionally, based on other genes, about 85 percent of people secrete a chemical signal through their skin that indicates which blood type they have, while 15 percent do not, and mosquitoes are also more attracted to secretors than nonsecretors regardless of which type they are. Read more: smithsonianmag.com/science-nature/…" $\endgroup$ – Mohammed Joraid Sep 4 '18 at 0:59
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Blood type is important only when mixing blood; the problem is parts of different immune systems getting into fights.

If the vampires don't have their own blood anymore, or their immune system works significantly differently than ours there won't be a problem even if the victim's blood is directly transfered.

Whatever mechanism vampirism uses to deal with a body's immune system in making a new vampire might plausibly work against blood from another body. A virus needs to be able to defeat the immune system, and magic obviously can handwave it away, if that's what you want.

Blood typing wasn't discovered until long after traditional vampire stories were established. It would be a very risky un-life for non-AB typed vampires if every meal was gambling with a transfusion rejection. But that could explain why they might stick with a single victim and take interest in dungeons or romance.

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Vampire don't drink blood because they need it to survive, but because they are addicted to blood, the same way a human is addicted to heroin or other hard drug.

But only the O- blood plainly works, the added elements in other blood type render the blood-drug either inefficient or this less efficient (if it fits your need it could allow the vampire to consume any type -even animal blood- as a succédané but it will always prefer the O- which is so much potent).

Note: this idea com from the discussion between @a4android and @Tim B (This solve the "It drinks blood, why? This plainly didn't make sense")

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