Blood tests show whether the levels of different substances in your blood fall within a normal range. For many blood substances, the normal range is the range of levels seen in 95 percent of healthy people in a certain group. For many tests, normal ranges are different depending on your age, gender, race, and... »

What To Expect Before Blood Tests Many blood tests don’t require any special preparation and take only a few minutes. Other blood tests require fasting (not eating any food) for 8 to 12 hours before the test. Your doctor will tell you how to prepare for your blood test(s). What To Expect During Blood... »

Von Willebrand disease (VWD) is a bleeding disorder. It affects your blood’s ability to clot. If your blood doesn’t clot, you can have heavy, hard-to-stop bleeding after an injury. The bleeding can damage your internal organs or even cause death, although this is rare. In VWD, you either have low levels of a certain... »

Thrombocythemia (THROM-bo-si-THE-me-ah) and thrombocytosis (THROM-bo-si-TO-sis) are conditions in which your blood has a higher than normal number of platelets (PLATE-lets). Platelets are blood cell fragments. They’re made in your bone marrow along with other kinds of blood cells. Platelets travel through your blood vessels and stick together (clot) to stop any bleeding that could... »

Rh incompatibility is a condition that occurs during pregnancy if a woman has Rh-negative blood and her baby has Rh-positive blood. “Rh-negative” and “Rh-positive” refer to whether your blood has Rh factor. Rh factor is a protein on red blood cells. If you have Rh factor, you’re Rh-positive. If you don’t have it, you’re... »

A pulmonary embolism (PULL-mun-ary EM-bo-lizm), or PE, is a sudden blockage in a lung artery. The blockage usually is due to a blood clot that traveled to the lung from a vein in the leg. A clot that forms in one part of the body and travels in the bloodstream to another part of... »