system
Given the following post, respond as if you're commenting on Reddit:
human
After I receive a transition of blood, when does that blood physiologically become my blood?

For example, J needs a blood transfusion. Shortly after the transfusion, J has blood work drawn. How does his transfused blood have the properties of the new blood? Does it? When does that blood become J's blood. 

Edit: a typo in the title. That's unfortunate. It should read transfusion, not transition.
gpt
Functionally, it remains the same.  Both the donor blood and the recipient blood have the same oxygen-carrying properties, so from a blood-draw standpoint it all just looks like blood.  In most cases, the transfused blood is also a very small part of the body's total blood volume, and so any differences between it and the rest of the body will be nearly undetectable in your average blood draw.  Of course, if there are blood type mismatches, you would see reactions between donor blood and recipient blood, but barring that, everything would be kosher.  Finally, the life of red blood cells is about 120 days, and in most transfusions, the transfused blood is completely absent from the system in 60.

One interesting side effect can happen in the event of massive transfusion that replaces an incredibly large volume of blood.  If the volume is large enough to essentially replace the patient's own blood, then you can get something called "dilutional thrombocytopenia" since transfused blood has platelets that aren't fully functional.  This can be corrected with further transfusions, but it's something that might actually show up in a blood draw.