What the risks are:

Veins and arteries vary in size from one patient to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Special considerations:

Current tests cannot tell for sure whether a low platelet count (thrombocytopenia) is caused by immune problems. Therefore, your doctor will make a diagnosis based on other tests and examinations.

This test is often performed because you have a bleeding problem. Bleeding may be more of a risk for you than for people who do not have bleeding problems.