Alkaline phosphatase

Topic Completed: 1 November 2013

Revised: 23 January 2020

Copyright: 2003-2018,, Inc.

PubMed Search: alkaline phosphatase[title]

Nat Pernick, M.D.
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Cite this page: Pernick N. Alkaline phosphatase. website. Accessed April 8th, 2020.
Definition / general
  • Membrane bound glycoprotein with hepatic, osseous, renal and placental isoenzymes
  • See also PLAP-placental alkaline phosphatase
  • Tissue-nonspecific alkaline phosphatase (TNAP) plays a key role in bone mineralization by degrading inorganic pyrophosphate and providing free inorganic phosphate
  • TNAP gene defect causes hypophosphatasia, characteristic of systemic skeletal hypomineralization
  • Surgical pathology applications discussed below
Clinical features
Uses by pathologists
  • Component of an alternative method in immunohistochemistry, click here
  • Muscle biopsies uses an enzymatic technique
    • Use frozen tissue (protocol from IHC World)
    • In inflammatory myopathies, appears to “spill out” from capillaries into interstitium due to increased vascular permeability
    • Also a marker for regenerating myofibers
  • Osteoblasts (active)
    • Often labeled using naphthol phosphate and the diazonium dye fast blue to demonstrate alkaline phosphatase enzyme activity directly, present on apical (secretory) cell membrane
    • Confirms diagnosis of giant cell tumor of bone (Virchows Arch A Pathol Anat Histol 1978;378:287)
Microscopic (histologic) images

Images hosted on other servers:

Muscle: various images

Muscle: immature
small fibers have
cytoplasmic staining

Positive staining - normal
  • Cardiac muscle, smooth muscle
  • Endothelial cells: sites of alkaline phophatase activity appear red, nuclei stain blue
  • Osteoblasts
Positive staining - disease
  • Giant cell tumor of bone and soft tissue, mononuclear stromal cells (Hum Pathol 2005;36:945)
  • Muscle: regenerating fibers, immature muscle fibers, proliferative connective tissues
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