Lactase Deficiency

Lactase deficiency is the lack of the activity of the enzyme lactase, which is required for digesting the disaccharide lactose, the primary carbohydrate in cow’s milk. Dietary lactose is hydrolyzed by small intestinal lactase to glucose and galactose on the microvillus membrane of the intestinal adsorptive cells.

It is the most common problem of carbohydrate digestion. It results mainly from the reduction of lactase activity in adults.

Genetic or familial lactase deficiency appears after 5 years of age.

Secondary lactase deficiency: The most common etiology is acute GI infection resulting in small intestinal injury with loss of lactase-containing epithelial cells at the tips of the villi

Symptoms & Signs

Diarrhea, abdominal distention, flatus, and abdominal pain after ingestion of milk or milk-containing products.


-Diagnostic tests include genetic testing and lactose breath test.

-The most widely available test for the diagnosis of lactase deficiency is the hydrogen breath test.

-Resolution of symptoms with lactose-free diet

-Patients with diarrhea have a stool osmotic gap of >125 mOsm/kg due to the presence of unabsorbed carbohydrates within the intestinal lumen and a stool pH <6 due to bacterial fermentation of lactose in the colon.


Dietary lactose restriction: Milk product avoidance

Enzyme replacement: Symptoms can be ameliorated by administration of commercial lactase preparations.

Calcium and Vitamin D: Patients who choose to restrict or eliminate milk products may have increased risk of osteoporosis. so, give calcium and vitamin D

Q: What does the breath hydrogen test measure? lactose malabsorption.

Q: Patient reports a recent history of Giardiasis, he was treated with metronidazole. Now, he reports abdominal pain, flatulence and diarrhea after milk products. What do you suspect? Lactose intolerance, which is a common complication of Giardiasis

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