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:

A serology test can determine if you have ever been exposed to a particular antigen, but this does not necessarily mean that you are currently infected. Increasing antibody levels over a 2-week period are more likely to indicate a current infection.