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Lactose intolerance
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Lactose intolerance

Contributors: Michael W. Winter MD, Christine Osborne MD, Khaled Bittar MD, Nishant H. Patel MD, Desiree Rivera-Nieves MD, Paritosh Prasad MD
Other Resources UpToDate PubMed


Lactose intolerance is a common malabsorption disease caused by insufficient lactase enzyme in the small intestine resulting in flatulence, diarrhea, bloating, and cramping abdominal pain after ingesting lactose-containing foods. The incidence of lactose intolerance varies among ethnicities, with patients of African, Asian, Native American, and Hispanic descent most affected.

Lactase deficiency can be primary, secondary, or congenital.
  • Primary – Low levels of lactase enzyme. Symptom onset may be in childhood or adulthood.
  • Secondary – Reversible lactase deficiency caused by mucosal injury, often in the setting of viral illnesses.
  • Congenital – A rare autosomal recessive absence of lactase activity at birth leading to diarrhea and hypercalcemia in infancy, predisposing patients to nephrocalcinosis.


E73.9 – Lactose intolerance, unspecified

782415009 – Intolerance to lactose

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Infectious Gastroenteritis (bacterial, Viral gastroenteritis, helminth)
  • Congenital lactase deficiency
  • Celiac disease
  • Small intestinal bacterial overgrowth
  • Inflammatory bowel disease (Ulcerative colitis, Crohn disease)
  • Irritable bowel syndrome
  • Generalized anxiety disorder
  • Biliary calculus
  • Chronic mesenteric ischemia
  • Chronic pancreatitis
  • Collagenous gastritis
  • Collagenous Colitis
  • Lymphocytic Colitis
  • Colon cancer
  • Food allergies
  • Malignancy: Gastric cancer, small bowel, or large bowel
  • Pancreatic carcinoma
  • Postcholecystectomy syndrome
  • Bile acid diarrhea
  • Somatostatinoma
  • Laxative abuse
  • Cow milk allergy

Best Tests

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Last Reviewed:01/10/2018
Last Updated:01/18/2022
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Lactose intolerance
A medical illustration showing key findings of Lactose intolerance : Abdominal pain, Diarrhea, Nausea, Vomiting, Abdominal cramp, Developed rapidly , Hyperactive bowel sounds, No acute distress
Copyright © 2024 VisualDx®. All rights reserved.