Colon (tumor & nontumor)
Noninfectious colitis
Pill fragment associated colitis

Topic Completed: 1 May 2016

Minor changes: 19 June 2020

Copyright: 2003-2020,, Inc.

PubMed Search: Kayexalate colitis

Raul S. Gonzalez, M.D.
Page views in 2019: 1,013
Page views in 2020 to date: 703
Cite this page: Gonzalez R.S. Pill fragment associated colitis. website. Accessed August 10th, 2020.
Definition / general
  • Sodium polystyrene sulfonate (Kayexalate) is an ion exchange resin that binds intraluminal potassium; it can cause ischemia and intestinal necrosis, especially (but not only) if given with sorbitol (Am J Surg Pathol 1997;21:60)
  • Sevelamer, used to treat hyperphosphatemia in patients with chronic kidney disease, binds phosphate and has may cause injury to the gastrointestinal tract (Am J Surg Pathol 2013;37:1686)
  • Bile acid sequestrants (e.g., cholestyramine) may microscopically mimic other pill fragments but do not appear to cause injury (Am J Surg Pathol 2014;38:1530)
Essential features
  • Kayexalate causes mucosal injury, and sevelamer may also as well
  • Other pill fragments (such as bile acid sequestrants) can also be identified microscopically, but do not cause mucosal injury
  • Colon is most commonly involved gastrointestinal organ, but any can be affected
  • Resins can rarely be encountered outside the gastrointestinal tract (due to perforation, aspiration, etc.) (Diagn Pathol 2008;3:27)
  • Microscopic examination and clinical confirmation of medication use
Case reports
Microscopic (histologic) description
  • Kayexalate: bright purple crystals with fish scale appearance
  • Sevelamer: yellow / pink crystals; also fish scale appearance
  • Bile acid sequestrants: opaque orange polygonal/rhomboid crystals; usually NO fish scale appearance; may be spherical (Histopathology 2015;67:141)
Microscopic (histologic) images

Images hosted on PathOut server:

Contributed by: Dr. Raul Gonzalez, University of Rochester Medical Center, New York (USA)

Images hosted on other servers:

Incidental luminal polystyrene
sulphonate resin particles in
jejunal diverticular tissue

Particles at site of colonic
necrosis (Direct Schiff stain
with light counterstain)

Particles at site of aspiration
pneumonia (Ziehl-Neelsen stain
with light counterstain)

Positive stains
  • AFB: Kayexalate appears black, sevelamer appears magenta, and bile acid sequestrants appear dull yellow
Differential diagnosis
  • Dystrophic calcification can mimic Kayexalate but is a brighter purple
  • Bile can mimic sevelamer but has no pink coloration
Additional references
Board review style question #1
Which of the following pill material fragments usually shows fish scales on histology?

  1. Colestipol
  2. Crospovidone
  3. Microcrystalline cellulose
  4. Sevelamer
Board review answer #1
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