Pediatric Lactose Intolerance Workup

The following laboratory studies are indicated in patients with lactose intolerance:

• Blood testing

  • The adult-type hypolactasia (most commonly caused by the CC genotype of the 13910 C/T polymorphism of the LCT gene) can now be easily diagnosed by a genetic analysis.
  • Studies have determined that genetic test results and breath test results are well-correlated, thereby eliminating the need for such testing.^[5]
• Stool analysis

  • Reducing substances in the stool indicate that carbohydrates are not being absorbed. One common mistake, especially with super-absorbent diapers, is to test the solid portion of the stool instead of the liquid portion.
  • Acidic stool is defined by a pH level of less than 5.5. This is an indication of likely carbohydrate malabsorption, even in the absence of reducing substances.

• Dietary elimination

  • Resolution of diarrhea and symptoms when a suspected substance is removed from the diet, as well as resumption of the diarrhea and symptoms when the substance is reintroduced, are very suggestive signs of intolerance.
  • Lack of diarrhea resolution when a substance is removed from the diet does not necessarily indicate tolerance. Malabsorption of one dietary component can result in diarrhea and subsequent malabsorption of other dietary components; thus, the sensitivity of this procedure can be low.
  • Conversely, resolution of symptoms upon withdrawal of lactose-containing foods from the diet may not confirm lactose intolerance. For instance, in the case of milk products, a patient can be sensitive to the milk proteins, and symptoms of such an allergy resolve once the milk or milk product is withdrawn from the diet.
• Hydrogen breath test

  • Carbohydrate malabsorption results in bacterial fermentation of the unabsorbed sugar. This biochemical process releases hydrogen gas that is absorbed into the blood and excreted by the lungs. In the absence of hydrolysis of lactose into its component monosaccharide sugars, galactose and glucose, lactose cannot be absorbed and passes into the large intestine. Thus, carbohydrate malabsorption can be determined by measuring the exhaled hydrogen concentration after a carbohydrate load is administered.
  • Under normal conditions, the fermenting bacteria reside only in the large intestine. When bacterial overgrowth in the small intestine occurs, upper small bowel fermentation of ingested but nonhydrolyzed lactose occurs and causes an early rise in the exhaled hydrogen concentration (>20 ppm). Under such conditions, an additional later rise in exhaled hydrogen occurs during large bowel fermentation.
  • Antibiotic administration may cause false-negative results. For diagnosis of lactose intolerance, 0.5-1 g/kg to 12-25 g of lactose is administered.
  • A trial on 60 subjects suspected of lactose malabsorption compared different breath tests and concluded that there was unsatisfactory agreement between commonly used diagnostic tests.^[6] The test with the best diagnostic properties was lactose breath test with 25 g lactose and measurement of the increase in the sum of H2 and CH4x2.

• Mucosal biopsy is almost never needed to diagnose lactose intolerance. However, it may prove useful as a part of the workup in patients with malabsorption of obscure cause. A small intestinal mucosal biopsy sample is obtained via endoscopy for direct assay of lactase activity and other brush border disaccharidases.
• The presence of small intestinal mucosal injury can also be assessed as a possible cause of secondary lactase deficiency.

• No abnormal histologic findings in the small intestinal mucosa are present in adult-type lactose intolerance and the exceedingly rare primary lactase deficiency.
• Villous blunting and lamina propria inflammatory changes are seen in cases of secondary lactase deficiency.