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Lab Test: Alkaline Phosphatase (ALP)

    Lab Test
    • Alkaline Phosphatase (ALP)
    Description
    • This test is used to detect and monitor diseases of the liver (specifically the biliary tract) and/or bone since ALP primarily originates from these tissues. It is also present in minor amounts in the intestine, kidney, and placental tissue.
    • Elevations in alkaline phosphatase should only be interpreted in conjunction with other clinical findings and diagnostic tests since it is not tissue or disease specific.
    Reference Range
    • Child/adolescent:
      • <2 years:  85-235 units/L
      • 2-8 years:  65-210 units/L
      • 9-15 years:  60-300 units/L
      • 16-21 years:  30-200 units/L
    • Adult:  30-120 units/L or 0.5-2.0 mkat/L (SI units)
    • Elderly:  slightly higher than adult
    Indications & Uses
    • Alkaline phosphatase (ALP) levels are greatly increased in both extra hepatic and intrahepatic obstructive biliary disease and cirrhosis.  Other liver abnormalities can include (hepatic tumors, hepatotoxic drugs, and hepatitis) and are generally associated with smaller elevations in ALP levels.
    • Isoenzymes of ALP can be used to distinguish between liver and bone diseases with ALP1 being higher in liver disease and ALP2 being high in bone disease.
    Clinical Application
    • Cholecystitis - in patients with hepatobiliary obstruction, an elevated alkaline phosphatase is observed in 30% t0 40% of patients,  The combination of a bilirubin level greater than 3 mg/dL with an alkaline phosphatase level greater than 250 IU/L has had a 76% probability of an associated common duct stone.  Alkaline phosphatase values typically return to normal within one week after symptoms resolve. 
    • Primary cirrhosis, intrahepatic or extra hepatic biliary obstruction, primary or metastatic liver tumor: It is normally excreted into the bile and any obstruction, even mild cases, can cause elevations in ALP.
    • Metastatic tumor to the bone, healing fracture, hyperparathyroidism, osteomalacia, Paget disease, rheumatoid arthritis, and rickets as the ALP comes from the bone in these diseases.
    • Intestinal ischemia or infarction
    • Myocardial infarction
    • Sarcoidosis
    Related Tests
    • Alanine aminotransferase (ALT) - can aid in the differential diagnosis of causes of ALP elevations.  If both are elevated, hepatocellular or hepatobiliary disease should be suspected. 
    • Aspartate aminotransferase (AST) - can aid in the differential diagnosis of causes of ALP elevation.  If both are elevated, hepatocellular or hepatobiliary disease should be suspected.
    • Gamma-glutamyl transpeptidase (GGT)- can aid in the differential diagnosis of causes of ALP elevation.  If both are elevated, diseases affecting the biliary tree should be suspected.
    • 5'-nucleotidase - can aid in the differential diagnosis of causes of ALP elevation.  If both are elevated, diseases affecting the biliary tree should be suspected.
    • Acid phosphatase - can aid in the differential diagnosis of causes of ALP elevation. 
    • Creatine kinase (CK)
    • Lactic dehydrogenase (LDH)- used to support the diagnosis of injury or disease involving the heart, liver, red blood cells, kidneys, skeletal muscle, brain, and lungs. 
    • Leucine aminopeptidase - specific to the hepatobiliary system.  Disease affecting that system will cause elevation of this enzyme.
    Drug-Lab Interactions
    • Recent ingestion of a meal can increase the ALP level
    • Age:  young children with rapid bone growth have increased ALP levels.  Most magnified during the growth spurt.  Females and males differ in age of growth spurt.
    • Drugs that may cause increased ALP levels:  albumin made from placental tissue, allopurinol, antibiotics, azathioprine, colchicine, fluorides, indomethacin, isoniazid (INH), methotrexate, methyldopa, nicotinic acid phenothiazine, probenecid, tetracycline, and verapamil.
    • Drugs that may cause decreased levels:  arsenicals, cyanides, fluorides, nitrofurantoin, oxalates, and zinc salts.
    Test Tube Needed
    • Obtain a 5 mL venous blood sample in red top tube.
    • Avoid use of an anticoagulant containing tube.
    Procedure
    • Collect a venous blood sample. 
    • Note the age and gender of the patient on test requisition. 
    • Apply pressure or a pressure dressing to the venipuncture site and assess the site for bleeding. 
    • Patients with liver dysfunction often have prolonged clotting times.
    Storage and Handling
    • Centrifuge and analyze within 2 hours of collection or refrigerate immediately
    What To Tell Patient Before & After
    • Explain the procedure to the patient and tell them that fasting is preferred (if feasible) since certain meals can elevated ALP and are generally higher after eating.
    References
    • Gordon T et al.  Factors associated with serum alkaline phosphatase level. Arch Pathol Lab Med 1993;117(2):187-90.  PMID; 8427569
    • LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests.  First ed. Montvale, NJ: Thomson PDR; 2007.
    • Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5th Ed.  St. Louis, Missouri. 2014.
    • Van Hoof VO et al. Age and sex distribution of alkaline phosphatase isoenzymes by agarose electrophoresis.  Clin Chem 1990;36(6):875-8.  PMID: 2357825
    •  Wallace BH et al.  Isoforms of alkaline phosphatase determined by isoelectric focusing in patients with chronic liver disorders.  Eur J Clin Chem Clin Biochem 1996;34(9):711-20.  PMID: 8891523

MESH Terms & Keywords

  • Alkaline Phosphatase (ALP), Liver Enzymes, Biliary Enzymes