Lactose intolerance diagnostic study of choice

Small bowel biopsy such as jejunal or duodenal biopsy is the gold standard test for the diagnosis of lactose intolerance. Low lactase activity in small bowel biopsy is confirmatory of lactose intolerance.The diagnostic study of choice for lactose intolerance is lactose breath hydrogen test. Lactose intolerance is diagnosed based on a rise in hydrogen concentration of 20 ppm ( parts per million) and the presentation of symptoms such as bloating, diarrhea and abdominal pain.

• Small bowel biopsy such as jejunal or duodenal biopsy is the gold standard test for the diagnosis of lactose intolerance via the investigation of lactase enzyme activity.^[1][2]
  • Low lactase activity in small bowel biopsy is confirmatory of lactose intolerance.
  • Distinguishes between primary and secondary lactase deficiency by evaluation of small bowel histology.
  • Nowadays, small bowel biposy is rarely performed and it is substitued with noninvasive diagnostic tests such as lactose tolerance test and lactose breath hydrogen test.

• The diagnostic study of choice for lactose intolerance is lactose breath hydrogen test. Following are a few important aspects related to lactose breath hydrogen test:^[3][4]
  • It is a noninvasive investigation
  • In adults, 50 g of lactose in water (equivalent to that in 1 L of milk), while in children, 2 g/kg of lactose (maximum dose 25 g) is administered in fasting state.^[5]
  • Breath hydrogen level and associated symptoms such as bloating, diarrhea and abdominal pain are checked at baseline and at 30 minute intervals for three hours.
  • Lactose malabsorption and intolerance are diagnosed based on a rise in hydrogen concentration of 20 ppm (parts per million) and the presentation of symptoms compared to baseline.
  • Undigested lactose is fermented by intestinal flora to carbon dioxide, hydrogen and methane and then they are eliminated via the lungs.
  • False negative result is due to:
    • Taking antibiotics within the previous month
    • Inhibition of bacterial activity by the more acidic environment of colon
    • Underlying lung disease
  • False positive result
    • Small bowel bacterial overgrowth:
      • Earlier rise in breath hydrogen level after the ingestion of lactose (less than 60 minutues)
      • Avoiding cigarette smoking and exercise 2 hours before lactose hydrogen test, because they cause hyperventilation and they can change accuracy of the test.^[6]

There are no established criteria for the diagnosis of lactose intolerance. However, investigations such as lactose breath hydrogen test and small bowel biopsy can be very helpful in the diagnosis of lactose intolerance.