A sample of your blood can reveal much about your health. But between the tests your doctor may order and the numerous new ones you can arrange yourself, it can be hard to know which are truly worth taking. by Hallie Levine You’re probably no stranger to having a nurse draw multiple vials of blood at annual check-ups. You might not think twice about this (except, ouch!). But once evaluated, these samples reveal how well important organs, such as your kidneys and liver, are functioning. Some blood tests can also help diagnose a health problem such as an infection or monitor chronic illnesses such as type 2 diabetes. …