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What is an Alkaline Phosphatase (ALP) test?

An ALP test measures the levels of Alkaline Phosphatase or ALP enzyme in the blood. This enzyme is found throughout the body but predominantly in liver, bones, kidneys and biliary duct.

It is produced by the cells that help in the formation of bone, ie, osteoblasts. Different tissues produce different forms of ALP isoenzymes. These isoenzymes can be distinguished on the basis of clinical signs and symptoms or by performing a test, which also helps in determining if any isoenzymes is increased in the blood.

Few conditions that can increase the amount of ALP in the blood are increased and rapid bone growth, which mainly occurs during puberty; bone disorders, such as Paget’s disease or bone cancer; hyperparathyroidism (a condition that affects calcium in the blood); vitamin D deficiency; and damaged liver cells.

The alternate terms for this test are ALP, Alk Phos, Alkp, alkaline phosphatase isoenzymes and bone-specific ALP test.

  1. Why is an ALP test performed?
  2. How do you prepare for an ALP test?
  3. How is an ALP test performed?
  4. What do ALP test results Indicate?

An ALP test is done to check the following disorders:

  • Liver disorders
  • Bone disorders, such as rickets, Paget’s disease, bone tumours or an increase in the parathyroid hormone

Few signs and symptoms that indicate liver involvement are:

Signs and symptoms that indicate bone involvement are:

ALP test can also be performed in some other condition. These include:    

  • Alcoholic liver disease such as hepatitis/cirrhosis
  • Alcoholism
  • Biliary stricture (abnormal narrowing of the bile duct)
  • Gallstones
  • Giant cell (temporal, cranial) arteritis (a disease of blood vessels)
  • Multiple endocrine neoplasia (MEN) II (a disorder in which endocrine glands become overactive and form a tumour)
  • Pancreatitis
  • Renal cell carcinoma (a type of kidney cancer)

Do not eat or drink anything for about 10 hours prior to the test as ALP levels can increase after eating fatty foods.

Inform your doctor if you are on any medication or supplements. He/she can advise you to stop certain medicines that can alter test results. Antibiotics narcotics, methyldopa, propranolol, cortisone, allopurinol, tricyclic antidepressants, androgens, tranquilisers, chlorpromazine, oral contraceptives (birth control pills), anti-inflammatory analgesics, antiarthritic drugs and oral antidiabetic drugs are few drugs that could affect ALP levels.

It is a simple procedure in which a blood sample will be withdrawn from a vein in your arm after swabbing the concerned area with an antiseptic solution.

After collection of the sample, the injection site will be pressed firmly, and a cotton ball or gauze pad will be placed over that area to stop bleeding. The collected blood sample will be further sent for examination.

Results of an ALP test can vary depending upon the method used and the age, gender, and health history of the individual. It is best to check in with a doctor to get the correct interpretation of results.

Normal results: The normal range of ALP for men and women older than 18 years is 37-116 units per litre (U/L).

Normal ranges for children and teenagers are:

  • For boys    
    • 1-3 years: 104-345 U/L
    • 4-6 years: 93-309 U/L
    • 7-9 years: 86-315 U/L
    • 10-12 years: 42-362 U/L
    • 13-15 years: 74-390 U/L
    • 16-18 years: 52-171 U/L
  • For girls    
    • 1-3 years: 108-317 U/L
    • 4-6 years: 96-297 U/L
    • 7-9 years: 69-325 U/L
    • 10-12 years: 51-332 U/L
    • 13-15 years: 50-162 U/L
    • 16-18 years: 47-119 U/L

Abnormal results: Higher levels of ALP can be seen in the following conditions:

  • Biliary obstruction (blockage of bile ducts)
  • Bone diseases or disorders
  • Osteoblastic bone cancers/tumours
  • Osteomalacia (softening of bones)
  • Healing fractures
  • Liver disease
  • Hepatitis
  • Hyperparathyroidism (over secretion of parathyroid hormone)
  • Leukaemia (cancer in blood-forming tissues)
  • Lymphoma (cancer in lymphocytes)
  • Paget’s disease
  • Rickets
  • Sarcoidosis (formation of granulomas in the body)
  • Anaemia

Lower levels of ALP can be seen in the following conditions:

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. Johns Hopkins Medicine [Internet]. The Johns Hopkins University, The Johns Hopkins Hospital, and Johns Hopkins Health System; Common Liver Tests
  2. Ellis E. Golub and Kathleen Boesze-Battaglia. The role of alkaline phosphatase in mineralization. Curr Opin Orthop 18:444–448. 2007 Lippincott Williams & Wilkins.
  3. MedlinePlus Medical: US National Library of Medicine; ALP - blood test
  4. Health Link. Alkaline Phosphatase. British Columbia. [internet].
  5. Lee Goldman Andrew Schafer. Goldman's Cecil Medicine. 24th Edition, SBN: 9781455753369
  6. Penn State Health. ALP isoenzyme test. Milton S. Hershey Medical Center; Pennsylvania
  7. Penn State Health. Gallstones. Milton S. Hershey Medical Center; Pennsylvania
  8. University of Rochester Medical Center. Alkaline Phosphatase. Rochester, New York. [internet].