A study of heart-attack patients just published online by the Archives of Internal Medicine finds that blood loss from diagnostic tests is associated with acquiring anemia in the hospital. And anemia -- a decrease in the red blood cells or in the specific protein that carry oxygen throughout the body– is associated with poorer health and a higher risk of death. The study looked at data from 17,676 heart-attack patients in 57 hospitals between 2000 and 2008. None of them had anemia when they were admitted, but over the course of their hospital stay 20% developed moderate-to-severe anemia. While it's impossible to prove causation with this type of study, those folks had a lot more blood taken than their counterparts who didn't acquire anemia in the hospital -- 174 milliliters over the course of a stay, compared to 84 mL. (A unit of blood, which is a bit less than a pint, is 450 mL.) For every 50 mL of blood drawn, the risk of moderate to severe anemia rose by 18%, researchers found.