What is the importance of "blood" in the novel, Turned (Book #1 in the Vampire Journals)?

Blood is what is sought after and consumed by Caitlin and the other vampires in the novel. Blood flows through the veins of human beings, and it is on this blood that Caitlin is desirous of feeding. The night of Carnegie Hall, she cannot help herself from devouring and feeding on Sergei Rakov, but a few days later, in the park, she is able to stop herself from feeding on a small child.