ALP (alkaline phosphatase) isoenzyme

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Blood test

A blood test to measure the amounts of different forms of alkaline phosphatase.

Alkaline phosphatase is an enzyme in the blood, intestines, liver, and bone cells. Its chemical structure varies (called isoenzymes) depending on where it is produced. This makes it possible to determine where a problem has originated. When bones are growing, liver cells are damaged, or a biliary obstruction occurs, alkaline phosphatase levels rise considerably.

Blood is drawn from a vein, usually from 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.

Fasting for 10 to 12 hours before the test is usually standard. A urine specimen may also be tested (your health care provider determines which tests are appropriate). Many drugs affect the level of alkaline phosphatase in the blood. These drugs will be monitored or you will be instructed to discontinue their use:

• Antibiotics
• Narcotics
• Methyldopa
• Propranolol
• Cortisone
• Allopurinol
• Tricyclic antidepressants
• Chlorpromazine
• Estrogens and progestins - oral contraceptives
• Anti-inflammatory analgesics - oral
• Male hormones
• Tranquilizers
• Some antiarthritic drugs
• Antidiabetics - oral

For infants and children: