China¡¯s rising demand for health care is exposing a chronic shortage of an essential commodity: blood.

With hospital blood supplies tight, desperate patients are turning to agents known as ¡°blood heads,¡± who sell certificates that give patients access to state blood banks, creating a black market at the heart of the health care system.

¡°To us patients, buying blood solves our problems,¡± said Hong, a retired Shanghai civil servant who suffers from myelodysplastic syndrome, a debilitating blood condition. ¡°If there were no blood heads, what would I do?¡±