Investigation

Tests

The most common cause of lactose intolerance is secondary lactose intolerance. The use of an Exclusion diet is the simplest diagnostic method:

• exclusion diet (low lactose) (symptom improvement) and then reintroduction (symptom recurrence). Usually improve within 48 hours of exclusion

More detailed investigation may be undertaken in some cases:

Diagnosis is often strongly suggested by the presence of reducing sugars in the stool.

Breath tests may also be used

• when colonic bacteria act upon undigested lactose, hydrogen is formed. Breath hydrogen analysis may be useful in the diagnosis of lactose intolerance

Notes:

• testing for reducing substances in the stools is not always helpful. Infants with positive reducing substances may have sufficient lactase activity
  • because lactase breaks down lactose into glucose and galactose, the presence of 20-25 milligrams per deciliter of glucose above fasting levels indicates sufficient levels of lactase