Alkaline Phosphatase

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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Lab Tests

Alkaline phosphatase, also known as ALP or Alk Phos, refers to a group of isoenzymes that are found in the bone, liver, intestines, skin, and placenta. The maximal activity of ALP is at a pH of 9.0-10.0. ALP is also a member of the metaloprotein family of enzymes, which are zinc dependent for their optimal function.[1], [2]


  • In the liver, ALP is formed by the liver and biliary mucoal cells and is excreted in the bile.
  • Elevated levels of ALP in the serum can be seen with any liver dysfunction
  • ALP of bone is the most common extra-hepatic source of increased ALP levels.

Patient Preparation

  • Fasting is preferred but not required
  • Overnight fasting may be required for isoenzymes
  • Factors which can cause increased levels:
  • pregnancy (especially the 3rd trimester), young children experiencing rapid growth, phenytoin use
  • Drugs: albumin made from placental tissue, allopurinol, antibiotics, azathioprine, colchicine, fluorides, indomethacin, isoniazid (INH), methotrexate, methyldopa, nicotinic acid, phenothiazine, probenecid, tetracycline, and verapamil
  • Factors which can cause decreased levels:
  • anticoagulated blood sample
  • Drugs: arsenicals, cyanides, fluorides, nitrofurantoin, oxalates, and zinc salts

Clinical Implications

Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country.[2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range 25-120 U/L 25- 120 U/L
Optimal Range 70- 100 U/L 70-100 U/L
Alarm Ranges <30 U/L or > 130 U/L <30 U/L or > 130 U/L

High levels indicate High levels can indicate:

Low levels indicate Low levels can indicate:

Associated Tests

Isoenzymes of ALP, Lactate Dehydrogenase and LDH isoenzymes, total bilirubin, AST, ALT, GGT, protein electrophoresis, total protein, serum albumin, serum globulin, WBC and differential, thyroid panel, serum calcium and serum phosphorus, bone markers


  1. Pagana Kathleen D, Pagana Timothy J (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain