ALP Bone Isoenzyme Test

Written by Elea Carey | Published on July 14, 2012
Medically Reviewed by Brenda B. Spriggs, MD, MPH, FACP

What Is an Alkaline Phosphatase Bone Isoenzyme Test?

ALP stands for alkaline phosphatase. ALP is an enzyme 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 is made.

Your bones make an isoenzyme called ALP-2. Levels of this enzyme increase when 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:

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

Why Has My Doctor Ordered This Test?

Doctors order an ALP-2 test if they are concerned you may have a bone disease.

Symptoms of bone disease include:

  • chronic bone and joint pain
  • bones that break easily or brittle bones
  • 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 six to 12 hours before the test. You may be asked to stop certain medications prior to 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 is important to tell your doctor about all the medicines you are taking. Include both prescription and over-the-counter drugs.

What Happens In The Test?

The ALP bone isoenzyme test is a blood test.

Your blood will be drawn by a nurse or laboratory technician.

A tourniquet will be tied around your upper arm. A vein will be located for the blood draw. The area around it will be cleaned. 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

According to the Mayo Clinic, the ALP bone isoenzyme range for healthy adults is 12.1 to 42.7 (Mayo Clinic)

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(rickets)
  • osteoporosis
  • Paget’s disease

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 below normal are sometimes found with:

  • malnutrition
  • anemia
  • estrogen use after menopause

However, high levels are much more common than low levels.

Follow-Up After the Test

The ALP bone isoenzyme test does not diagnose any disease on its own. It can only narrow down the list of causes for your symptoms.

If you have a positive test, further tests will probably be necessary. These will determine what type of bone disease you may have.

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Show Sources

  • Taylor, J.A., Richter, M, Done, S., & Feldman, K.W. (2010, December). The utility of alkaline phosphatase measurement as a screening test for rickets in breast-fed infants and toddlers: a study from the Puget Sound Pediatric Research Network. Clinical Pediatrics 49(12):1103-10. Retrieved July 13, 2012, from

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