The blood of a vampire is a culmunation of the blood of all its victims, with some of that blood being used up to keep the vampire alive giving you the reason to drink blood in the first place.

The problem is that the vampire is mixing blood types. Blood type A+, A-, B+, B-, O+, O-, AB+ and AB- will all have a chance to be present. Mixing blood types is dangerous for humans as these blood types will clump together and block blood vessels.

In order to have useful blood the vampires have something in their blood, either mystical or physiological, that prevents this cluttering. Someone taking a blood test could notice this. You have some options:

• the blood loses its mystical protection and immediately clumps together, revealing something's up. Blood typing is done by mixing an A or B type blood and seeing when it starts clumping, so an immediate clumping before you add something is rather surprising.
• the blood keeps its mystical protection and never clumps, protecting the identity of the vampire
• the physiological protection keeps the blood from clumping. This is likely not discovered through any regular blood tests as no clumping means an AB blood type. Some tests can be done that forces AB blood to clump, if that doesn't happen it will reveal the oddity of the vampire blood.
• the physiological protection fails and blood starts to clump.
• the physiological protection is a rather obvious part of the blood, perhaps changing its color when outside the body or a similar trait, revealing the vampire.

Choice is yours.

The blood of a vampire is a culmunation of the blood of all its victims, with some of that blood being used up to keep the vampire alive giving you the reason to drink blood in the first place.

The problem is that the vampire is mixing blood types. Blood type A+, A-, B+, B-, O+, O-, AB+ and AB- will all have a chance to be present. Mixing blood types is dangerous for humans as these blood types will clump together and block blood vessels.

In order to have useful blood the vampires have something in their blood, either mystical or physiological, that prevents this cluttering. Someone taking a blood test could notice this. You have some options:

1. the blood loses its mystical protection and immediately clumps together, revealing something's up. Blood typing is done by mixing an A or B type blood and seeing when it starts clumping, so an immediate clumping before you add something is rather surprising.
2. the blood keeps its mystical protection and never clumps, protecting the identity of the vampire
3. the physiological protection keeps the blood from clumping. This is likely not discovered through any regular blood tests as no clumping means an AB blood type. Some tests can be done that forces AB blood to clump, if that doesn't happen it will reveal the oddity of the vampire blood.
4. the physiological protection fails and blood starts to clump.
5. the physiological protection is a rather obvious part of the blood, perhaps changing its color when outside the body or a similar trait, revealing the vampire.

Choice is yours.

The blood of a vampire is a culmunation of the blood of all its victims, with some of that blood being used up to keep the vampire alive giving you the reason to drink blood in the first place.

The problem is that the vampire is mixing blood types. Blood type A+, A-, B+, B-, O+, O-, AB+ and AB- will all have a chance to be present. Mixing blood types is dangerous for humans as these blood types will clump together and block blood vessels.

In order to have useful blood the vampires have something in their blood, either mystical or physiological, that prevents this cluttering. Someone taking a blood test could notice this. You have some options:

• the blood loses its mystical protection and immediately clumps together, revealing something's up. Blood typing is done by mixing an A or B type blood and seeing when it starts clumping, so an immediate clumping before you add something is rather surprising.
• the blood keeps its mystical protection and never clumps, protecting the identity of the vampire
• the physiological protection keeps the blood from clumping. This is likely not discovered through any regular blood tests as no clumping means an AB blood type.
• the physiological protection fails and blood starts to clump.
• the physiological protection is a rather obvious part of the blood, perhaps changing its color when outside the body or a similar trait, revealing the vampire.

Choice is yours.

The blood of a vampire is a culmunation of the blood of all its victims, with some of that blood being used up to keep the vampire alive giving you the reason to drink blood in the first place.

The problem is that the vampire is mixing blood types. Blood type A+, A-, B+, B-, O+, O-, AB+ and AB- will all have a chance to be present. Mixing blood types is dangerous for humans as these blood types will clump together and block blood vessels.

In order to have useful blood the vampires have something in their blood, either mystical or physiological, that prevents this cluttering. Someone taking a blood test could notice this. You have some options:

• the blood loses its mystical protection and immediately clumps together, revealing something's up. Blood typing is done by mixing an A or B type blood and seeing when it starts clumping, so an immediate clumping before you add something is rather surprising.
• the blood keeps its mystical protection and never clumps, protecting the identity of the vampire
• the physiological protection keeps the blood from clumping. This is likely not discovered through any regular blood tests as no clumping means an AB blood type. Some tests can be done that forces AB blood to clump, if that doesn't happen it will reveal the oddity of the vampire blood.
• the physiological protection fails and blood starts to clump.
• the physiological protection is a rather obvious part of the blood, perhaps changing its color when outside the body or a similar trait, revealing the vampire.

Choice is yours.