How the test is performed: Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test: Consult the health care provider about the need to take (or not take) your usual dose of medication before the test.
How the test will feel: When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed: The main purpose of this test is to monitor patients taking digitalis medications such as digitoxin in order to determine the effective drug dosage and prevent toxicity. Monitoring the drug level is important because the margin of safety between therapeutic levels and toxic levels is narrow.
Normal Values: Normal therapeutic values are 10 to 30 ng/ml. Toxicity is associated with values greater than 45 ng/ml.
Note: ng/ml = nanograms per milliliter
What abnormal results mean: - medication dosage is excessive or inadequate
- digitalis toxicity is present or is likely to develop (elevated value)
What the risks are: The risks associated with having blood drawn are:
- excessive bleeding
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
Special considerations: 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.
