Stains & CD markers
Alkaline phosphatase

Editor-in-Chief: Debra L. Zynger, M.D.
Chunyu Cai, M.D., Ph.D.

Last author update: 16 April 2020
Last staff update: 17 June 2021

Copyright: 2003-2023,, Inc.

PubMed Search: alkaline phosphatase [title] stain pathology

Chunyu Cai, M.D., Ph.D.
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Cite this page: Cai C. Alkaline phosphatase. website. Accessed September 30th, 2023.
Definition / general
  • An enzyme histochemical stain that relies on endogenous alkaline phosphatase activity to hydrolyze exogenous alpha naphthyl acid phosphate substrate to form naphthol, which in turn reacts with fast blue RR salt to form a black reaction product (Zhou: A Case-Based Guide to Neuromuscular Pathology, 1st Edition, 2020)
  • Alkaline phosphatase reaction generates air bubbles if the section is cover slipped prematurely; to minimize this, it is advisable to wait at least 45 minutes before placing the coverslip over the stained section
Essential features
  • Other names: Gomori alkaline phosphatase stain, nonspecific alkaline phosphatases
  • Assess for black reaction product
Uses by pathologists
Prognostic factors
Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Chunyu "Hunter" Cai, M.D., Ph.D.

Normal muscle

Dermatomyositis Mi2

Dermatomyositis NXP2

Antisynthetase syndrome PL7

Antisynthetase syndrome Jo1

Necrotizing autoimmune myopathy HMGCR

Reducing body myopathy

Positive staining - normal
Positive staining - disease
Negative staining
  • Myofibers undergoing active necrosis or phagocytosis
  • Duchene muscular dystrophy, limb girdle muscular dystrophy or experimental ischemic myopathy do not show perimysial connective tissue reactivity (Am J Pathol 1980;101:159)
Board review style question #1

In a normal muscle biopsy specimen, which of the following components stains for alkaline phosphatase?

  1. Arterioles
  2. Capillaries
  3. Connective tissue
  4. Muscle fibers
  5. Venules
Board review style answer #1
A. Arterioles

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