What the risks are:

The risks of the test are minimal and are related to the blood draw process. Rarely, the following will occur:

• Excessive bleeding at blood draw site
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

Special considerations:

Factors that may interfere with the accuracy of the test are as follows:

• Incomplete urine collection
• Pregnancy or vigorous exercise

Drugs that can interfere with creatinine clearance measurements include: cimetidine, trimethoprim, and nephrotoxic drugs, such as cephalosporins (cefoxitin).

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.