Some are so broad they encompass nonliving entities, such as fire or mineral crystals. Others are so narrow they disqualify mules, which are sterile. If you don t believe in Darwinian evolution, then nothing is alive according to that definition. If you do believe that the various blood types all evolved from a more primitive blood type, then blood may be alive, depending upon your definition of self-sustaining. A few days after you get sunburned, you might peel off some dead skin.
Reproduction usually figures into a definition of life somehow.
When skin grows it must be reproducing itself. But blood doesn t reproduce itself. Blood is manufactured by bone marrow. That makes it more like milk, which is manufactured by mammary glands. In this case, we can t measure what we are speaking about.