Key Symptoms:

Common: Intermittent diarrhea, gas, bloating, abdominal pain.
Less Common: Irritability, fecal soiling, nausea.
Symptoms may not occur every time you drink milk or have milk products. 
The Lactose Breath Test is a useful test for children and adults who have Lactose Intolerance

Lactose Intolerance

Lactose intolerance is a common cause of abdominal pain in children. In children less than five years of age, lactose intolerance is uncommon unless associated with a recent viral infection of the GI tract. In children over five, lactose intolerance begins to occur naturally as production of the enzyme Lactase at the intestinal brush border falls off with age. Classically, lactose intolerance causes gas, abdominal pain, urgency and diarrhea. However, even with daily ingestion of lactose, symptoms may be both variable and intermittent, making it difficult for both the patient and their physician to relate symptoms to lactose. Compounding the difficulty in diagnosis is the fact that some children have non-classical symptoms, such as vague abdominal discomfort without diarrhea, or discomfort in class with difficulty concentrating or irritabily. Children with attention related disorders may even soil their underwear, probably  because of the sudden, uncontrollable urge to have a bowel movement from the build-up of gas and liquid stool. For many children, temporarily eliminating milk and milk products, or the use of lactose digesting enzymes such as Lactaid, is sufficient to eliminate symptoms. However, some people may be quite sensitive to even small amounts of lactose present in a variety of foods such as prepared soups, breads, crackers and even medications. Restriction of these products without a specific diagnosis is difficult. Also, since the association between ingestion of lactose and pain is quite variable in a lactose intolerant child, parents may have difficulty limiting lactose-containing foods that are enjoyed by their child without confirming the diagnosis. In these latter patients, a lactose breath test may be helpful.

Lactose Breath Test

The lactose breath test is a simple, non-invasive test for lactose intolerance. It can be performed on patients from infancy to adulthood. The patient is given a flavored solution of lactose in water and breath samples are taken every 15-30 minutes for 2 to 3 hours. Malabsorbed lactose is converted by colonic (large intestinal) bacteria to hydrogen which is absorbed by colonic epithelium (surface lining cells) and rapidly excreted in breath. The patient breathes into a a balloon-like bag and the gas collected in injected into a sensitive gas chromatogram that the measures the increase in hydrogen. The tests results are availabe immediately. If the patient is lactose intolerant, a strict lactose free diet is prescribed. If all symptoms resolve, no further testing is necessary and the diet can be gradually liberalized with lactose containing foods as tolerated.

Lactose Intolerance versus Milk Allergy

Lactose intolerance should not be confused with milk allergy. Milk allergy results from a true allergy to the protein in milk. Milk allergy may cause diarrhea, but it also may cause wheezing, eczema, hives or vomiting. On the other hand, lactose intolerance is related to the inability to absorb the sugar(lactose) in milk. This may cause gas, diarrhea, bloating and abdominal discomfort, but not the other more serious symptoms mentioned with milk protein allergy. Milk protein allergy is common in children less than one year of age; these children require non-milk based formulas that are either soy based or contain milk that is hydorlyzed or broken down to non-allergic components (Nutramigen, Alimentum); lactose intolerance (except when associated with a viral infection) is uncommon in infants, but is quite common in older children and adults.