According to a recent post on Hirhurim, the frum vampire community is suffering from a blood crisis. There also appears to be much confusion as to the halakhic specifications regarding the consumption of human blood, which as we all know is an essential component of the vampire diet. It is also well known that many in the vampire community are not meticulous in their mitzvah observance, and it is my opinion that this is largely precisely due to certain misconceptions about what the halakha might or might not allow them.
For these reasons, and noting as it hasn’t been taken up by contemporary poskim yet, I have taken upon myself to clarify the halakha. If one should not wish to read the entire article, I would advise to simply skip to the last paragraph and note my conclusions, which I believe may be relied upon by all vampires l’khatḥila, halakha l’ma’aseh.
The Gemara says:
אמר רב ששת דם מהלכי שתים אפילו מצות פרוש אין בו
R. Sheshet said: Blood of two legged creatures [Rashi: humans] is not subject to a commandment of refraining from. 
From here it would seem that it is perfectly permissible for one to consume human blood. Yet the Gemara also says there:
תניא דם שעל גבי ככר גוררו ואוכלו של בין השינים מוצצו ובולעו ואינו חושש
We learned in a Baraita: Blood that is on top of a loaf, one may scrape off and eat [the loaf]. That which is between the teeth one may suck out and swallow, and not worry.
Why in the case of the loaf does one have to scrape off the blood? Rashi in Ketubot explains:
דמדפריש אסור מדרבנן דמיחלף בדם בהמה ואתי למימר דם בהמה אכל
When the blood has separated [from the body] it is rabbinically forbidden, for it might be confused with blood of an animal [which is forbidden], and they might say “he ate the blood of an animal.” 
It seems that the only halakhic issue with the consumption of human blood is that of mar’it ayin; that it might appear to the onlooker that it is animal blood being consumed. Indeed, this is how the halakha is codified in the Shulhan Arukh:
דם אדם אם פירש ממנו אסור משום מראית עין
Blood of a person is forbidden due to mar’it ayin.
In the Tur there is one extra word in that sentence:
ודם אדם אם פירש ממנו אסור גם כן משום מראית העין
Blood of a person is also forbidden due to mar’it ayin.
What is the “also” referring to? It is saying that this is an extension of the previous halakha, which reads:
דם דגים אף על פי שהוא מותר אם קבצו בכלי אסור משום מראית העין
Blood of fish, even though it is permitted, if one gathered it in a vessel it is forbidden due to mar’it ayin.
It is apparent from here that the halakha equates the blood of humans with the blood of fish. The significance of this is the fact that there is a special clause mentioned at the end of the fish halakha:
לפיכך אם ניכר שהוא מדגים כגון שיש בו קשקשים מותר
Therefore, if it is noticeable that it is from fish – such as if there are scales inside it – it is permitted.
If it is noticeable that it is not the blood of animals, there is no concern for mar’it ayin, and therefore the blood of fish would be permitted in such a case. The logical conclusion from here is to say that human blood as well, if it is noticeable that it is not animal blood, would be permitted, because as we have seen the halakha equates human blood with fish blood.
R. Akiva Eiger points out that the sugya in the Gemara seems to indicate that the heter of scales only applies when the scales were in the fish blood to begin with. However, he concedes that Rema is quite clear later on that the heter of scales would even apply to where one placed some scales next to a vessel of fish blood as a sign that it is only the blood of fish. We see from here that l‘halakha the siman being used to show that this is not animal blood can be placed there after the fact.
[He also points out that the Gemara seems to assume that the scale heter doesn’t apply to human blood. This is part of his proof that one cannot simply place the scales there later, for if one could, why couldn’t one simply put scales next to human blood too? Although this is a fair question, he himself notes that Rema disagrees with this understanding of the sugya. Also, I think that one could answer that it is possible that scales are not a viable heter for human blood, because all scales do is say that this is fish blood, not that this isn’t animal’s blood. It is possible that one can distinguish between fish blood and human blood, and therefore with human blood scales will not suffice to preclude mar’it ayin, because no one will make the connection from the scales to the blood to realize that this blood is not animal blood. At any rate, the halakha which seems clear is that as long as there is a siman or a היכר that the blood is only human, it would be permissible for consumption.]
R. Akiva Eiger points out one added note, that Rema would permit such blood even without a siman, if it is cooked, since the reasoning behind the issur d’rabbanan is that it might be confused with animal blood, and cooked animal blood is only a d’rabbanan anyway, and we would not issue a decree on top of another decree in this instance.
From here we can solve the blood crisis of the vampires. As long as there is a hekhsher on the packaging, it can be assumed that any observers know full well that the blood being consumed is human. Therefore one needs only to leave the container out during times of consumption. This would then be comparable to placing scales on the table next to the vessel of fish blood. If for some reason no hekhsher-ed blood is available, there are two options, either one may place an easy to read sign on the table identifying the blood as human, or one can cook it.