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.

No special preparation is necessary.

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.

Serum prolactin is usually measured as part of the diagnostic work-up of pituitary tumors, irregular menstrual periods, infertility, impotence, and galactorrhea (breast milk production that isn't related to childbirth).

Prolactin is a protein hormone secreted from the anterior pituitary gland. Prolactin stimulates breast development and milk production in women. There is no known normal function of prolactin in men.

The normal values for prolactin are as follows:

• Males and nonpregnant females: 0 to 20 ng/ml
• Pregnancy: 10 to 300 ng/ml

Prolactin levels can be elevated in the following conditions:

• Prolactinomas (a pituitary tumor that makes prolactin)
• Other pituitary tumors and disease
• Hypothalamic disease
• Hypothyroidism
• Kidney disease
• Chest wall trauma or irritation
• Medication-related (estrogens, tricyclic antidepressants, metoclopramide, phenothiazines, butyrophenones, reserpine, methyldopa, H2 blockers)

If your prolactin levels are elevated, the test may be repeated following an 8-hour fast.

• Excessive bleeding
• 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

• 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.
• Stress, recent exercise, and a recent breast examination can temporarily increase prolactin levels.