What is Bone Specific Alkaline Phosphatase?

Alkaline phosphatase (ALP) is an enzyme that’s naturally present throughout your body. It comes in many variations called isoenzymes. Each isoenzyme of ALP is different, depending on where in your body it’s made.

Your bones make an isoenzyme called ALP-2. Levels of this enzyme increase when your bones are growing or bone cells are active.

An ALP bone isoenzyme test can detect abnormal levels of bone growth that may be associated with conditions such as:

• Paget’s disease of bone
• certain bone cancers
• osteoporosis

Other names for an ALP bone isoenzyme test include:

• an ALP-2 test
• bone-specific alkaline phosphatase test
• bone-specific ALP test

What’s the purpose of this test?

Your doctor may order an ALP-2 test if they’re concerned you may have a bone disease.
The symptoms of the bone disease include:

• chronic bone and joint pain
• bones that are brittle or break easily
• deformed bones

An ALP-2 test can also be used to monitor bone disease treatment.

What do I need to do to get ready for the test?

Your doctor may tell you not to eat or drink anything for 6 to 12 hours before the test. You may be asked to stop certain medications before the test. Follow your doctor’s orders carefully. Your test results could be incorrect if you don’t.
Certain drugs may affect ALP-2 levels. These include:

• aspirin
• birth control pills
• antibiotics
• estrogen

It’s important to tell your doctor about all the medicines you’re taking. This includes both prescription and over-the-counter drugs.

How does the test work?

The ALP bone isoenzyme test is a blood test.
A nurse or laboratory technician will draw your blood. They will tie a tourniquet around your upper arm and locate a vein inside your elbow for the blood draw. Next, they’ll clean the area around it. A needle will be inserted, and blood will be drawn into a small vial. You may feel a slight pinch. Your blood will be sent to a lab for diagnosis.

Sometimes, blood may be taken from a vein on the back of your hand instead of from one inside your elbow.

Interpreting test results

The ALP bone isoenzyme range for healthy adults is 12.1 to 42.7.

Children have higher levels of ALP bone isoenzyme. ALP-2 is also elevated in people with broken bones. In both groups, bone growth is expected and normal.

Higher-than-normal levels of ALP bone isoenzyme could indicate a bone disease such as:

• osteoblastic bone tumors
• osteomalacia, or rickets
• osteoporosis
• Paget’s disease of bone

An elevated test result could also indicate serious conditions such as hyperparathyroidism or leukemia. Both diseases affect your bones as well as other parts of your body.

Test results that are below normal are sometimes found in people with malnutrition or anemia. Results that are below normal can also be found in women who take estrogen after menopause. However, high levels are much more common than low levels.