Lactose hydrogen breath test
This is a simple, noninvasive test wherein the patient receives a lactose load and the breath is measured for hydrogen every 15 to 30 minutes for up to 3 hours. The test looks for increased levels of hydrogen, which normally peaks in 90 to 120 minutes following the load. At 78% and 98%, respectively, the sensitivity and specificity are superior to the absorption test.11 It is considered the most reliable and cost-effective test for diagnosing lactose malabsorption.12 This test has largely replaced the lactose tolerance test if testing is needed.
The test is noted to be more reliable than history alone because patients think they are lactose intolerant and turn out not to be, and vice versa.2
Recent antibiotics, high-fiber diets, small intestinal bacterial overgrowth, intestinal motility disorders, and a lack of hydrogen-producing bacteria in the gut can lead to false-positive and false-negative results.2
Postprandial hypoglycemia is considered a contraindication. Although uncommon, migraines, stomach cramping, panic attacks, dizziness, and allergy-like reactions all have been reported as adverse effects of testing, and anyone performing these tests should be prepared to address them.12
Lactose tolerance test
In this more-invasive test, children are administered a lactose load (2 g/kg). Blood glucose levels are monitored at 0, 60, and 120 minutes. Development of symptoms with an increased blood sugar of 20 mg/dL is diagnostic. In adult populations, the sensitivity and specificity are reported as 75% and 96%, respectively.13 In general, the lactose tolerance test is no longer deemed appropriate for clinical practice.6
Small bowel biopsy and genetic testing are also available. Small bowel biopsies are rarely performed because of the availability of the sensitive and specific noninvasive tests mentioned above. Likewise, genetic tests for malabsorption are rarely performed because of cost.
Ruling out other causes
Because symptoms of lactose intolerance are vague, children should be evaluated for secondary causes, including:
· Bacterial overgrowth;
· Infectious (eg, Giardia);
· Celiac disease;
· Inflammatory bowel disease such as Crohn disease; and
· Prematurity/developmental lactase deficiency.
Ingestion of large amounts of sorbitol or other simple carbohydrates can lead to osmotic diarrhea and symptoms similar to lactose intolerance. In older adolescents, the pediatrician may need to also consider surreptitious laxative use. Finally, the pediatrician should consider cow’s milk allergy in patients who continue symptoms after lactose restriction.