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Alkaline Phosphatase Medical Background

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Medical Background

Source & biological action

ALP is not a single enzyme; its activity represents the sum of individual activities of intestinal, placental and hepatic-bone-renal ALP, postgenetic forms including biliary-duct ALP and tumor phosphatases. These membrane-bound isoforms of glycoproteins share a common protein structure but differ in carbohydrate content. All isoforms of ALP are involved in metabolite transport across cell membranes. ALP values represent the sum of the single activities that are present in the different organs and tissues.

Indications for testing

Suspicion of biliary involvement in the diagnosis of liver diseases:

• Cholestatic liver disease
• Liver parenchymal disease with associated cholestasis

Suspicion of skeletal disease:

• Bone disease
• Skeletal involvement as a consequence of other primary diseases

Patient preparation

• Fasting is preferred but not required for the test

Determination

ALP can immediately be determined in capillary or venous whole blood, plasma or serum in the physician's office with Reflotron® Plus or Reflotron® sprint using Reflotron® Alkaline Phosphatase.

Results

Reference ranges (Reflotron®) *

Temperature	Men	Women
25°C, 30°C, 37°C	40 - 129 U/l	35 - 104 U/l

* please refer also to the Reflotron® test package insert

Note:

• In children and adolescents ALP values are higher because of an increased osteoblastic activity associated with bone growth.
• Raised serum total ALP may be observed in women during the third trimester of pregnancy, due to high amounts of ALP present in the placenta.
• After age 60, reference limits increase in women and may become similar or even higher than in men.

Interpretation

Conditions with elevated ALP

• (Liver ALP)
  • Cholestasis, cholecystitis, cholangitis, cirrhosis, hepatitis, fatty liver, liver tumor, liver metastases, drug intoxication
  • Drugs: e.g. verapamil, carbamazepine, phenytoin, erythromycin, allopurinol, ranitidine
• Bone disease (Bone ALP)
  • Paget's disease, osteosarcoma, bone metastases of prostatic cancer (High / very high ALP values)
  • Other bone metastases
  • Multiple myeloma
• Skeletal involvement of other primary diseases
  • Osteomalacia, rickets, vitamin D deficiency (Moderate rise)
  • Malign tumors (ALP originating from tumor)
  • Renal disease (secondary hyperthyroidism)
  • Primary hypothyroidism

Conditions with low ALP

• Genetic hypophosphatasemia
• Adynamic bone disease in dialysis patients
• Hypoparathyroidism
• Malnutrition
• Drugs: e.g. clofibrate, oral contraceptives

Tips & recommendations

• ALP levels are higher depending on the completeness of biliary occlusion. Liver disease with primary damage to parenchymal cells usually causes only moderate rises in activity, the level depending on the degree of associated cholestasis.
• Unexplained ALP elevations should be further investigated by testing for g-glutamyltransferase (GGT), glutamic-oxaloacetic transaminase (GOT), and glutamic-pyruvic transaminase (GPT).
• In most cases you may not need expensive differentiation of ALP isoforms.

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