There are two tests that can help identify the condition. The first is a stool acidity test, which is generally given to infants and young children to determine the amount of glucose and lactic acid in their stools. A higher amount indicates the inability to digest lactose. The other test is a hydrogen breath test. Essentially, you drink a milk-based beverage and the undigested lactose creates a high level of hydrogen, which is measurable in your breath. 

How and When Lactose Intolerance Develops 

Over time, symptoms of lactose intolerance may worsen. Many times people don't have full-blown symptoms until adulthood, even though the condition may begin in early childhood. In some cases, secondary lactose deficiency may occur following injury to the small intestine, reports the NDDIC, which may be related to infection or disease. 

Further, congenital lactase deficiency is a rare genetic disorder in which the small intestine does not produce lactase enzymes at the time of birth, or produces very little. Finally, some children may have developmental lactase deficiency, which is present at birth in children born prematurely but may go away after a short time. 

Though African-Americans, Asian-Americans, Hispanics and American Indians have a higher risk of developing lactose intolerance, it is a fairly common condition among all adults, regardless of their race, ethnicity or family history.